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The announcement of an enhanced role for the military came as officials in President Hosni Mubarak’s government suggested a momentous shift in power was underway, including a possible transfer of power from Mr. Mubarak to his Vice President Omar Suleiman.

Hossan Badrawi, secretary general of the National Democratic Party (NDP), told Egyptian state news outlets and the BBC that Mr. Mubarak would “most probably” speak to the nation soon, and that he would likely step down from his post.

In testimony before the House Intelligence Committee, C.I.A. Director Leon E. Panetta said that there was a “strong likelihood” that Mr. Mubarak would step down by the end of the day.

Although the shape of a new Egyptian government remained unclear, television images on Al Jazeera showed the masses in Tahrir Square cheering the news of an impending shake-up, waving flags and chanting: “The Army and the people in one hand.”

Vice President Omar Suleiman, named by Mr. Mubarak to undertake a dialogue with opposition groups, had warned Tuesday night that if the process he was supervising did not produce results, the military would step in to take administrative control in what he called a “coup.” He did not say what role he would play in a military government.

The announcement came as Egypt’s uprising entered its 17th day on Thursday, bolstered by strikes and protests among professional groups in Cairo and workers across the country. A senior official in Mr. Mubarak’s embattled government was quoted as saying the army would “intervene to control the country” if it continued to devolve into chaos.

As tension built ahead of Friday’s planned mass protests, thousands of chanting lawyers in black robes and physicians in white laboratory coats marched into Tahrir Square — the epicenter of the uprising — to join the clamor for Mr. Mubarak’s ouster.

Engineers and journalists also headed for the square on Thursday as the numbers there began to swell once again into the thousands, with demonstrators mingling among the tents and graffiti-sprayed army tanks that have taken on an air of semipermanence.

Officials in Mr. Mubarak’s government have been warning for several days that protesters faced a choice between negotiating in earnest with the government on Constitutional changes or having the military step in to guard against a descend into political chaos. Foreign Minister Ahmed Aboul Gheit seemed to add a further ominous tone to those comments today, telling Al Arabiya television,

“If chaos occurs, the armed forces will intervene to control the country, a step which would lead to a very dangerous situation.”

Mr. Aboul Gheit made the comments a day after he dismissed calls by Egyptian protesters and Vice President Joseph R. Biden Jr. to scrap the country’s emergency laws, which allow the authorities to detain people without charge.

Up until now, the military has pledged not to use force against the protesters who have occupied Cairo’s central Tahrir Square and whose tactics have broadened to the establishment of a fresh encampment outside the Egyptian Parliament. But a report released Thursday by Human Rights Watch cast doubt on the military’s impartiality.

“Since Jan. 31, Human Rights Watch has documented the arbitrary arrest by military police of at least 20 protesters who were leaving or heading to Tahrir Square,” the group said in a statement. “Most of these arrests occurred in the vicinity of the square or in other parts of Cairo from where protesters were taking supplies to the square.”

The group said it had also documented at least five cases of the torture of detainees at the hands of the military. A spokesman for the military denied the accusations.

The army has also deployed tanks and reinforcements across the city, setting up a narrow access point to the square that forces would-be protesters into single file after they stand in long lines to enter.

The apparently hardening official line — and the stubborn resistance of the protesters — coincided with a surge of strikes and worker protests affecting post offices, textile factories and even Al Ahram, the government’s flagship newspaper.

While the government turned up pressure on the opposition, there were continued signs of turmoil within its own ranks. State TV reported that the state prosecutor had opened a formal investigation of Ahmed Ezz, a widely hated former senior member of the ruling National Democratic Party and a confidant of the president’s son Gamal Mubarak, and two other former ministers.

Another N.D.P. official, Mamdouh Hosny, director of the Industry and Energy Committee in Parliament, announced he was resigning from the party, the Egyptian daily, Al Masry Al Youm, reported.

The presence of lawyers and other professionals joining the demonstrations seemed to broaden the participation in the uprising, reflecting the influence of the Muslim Brotherhood, which has strong support among Egyptian lawyers and other professions..

Some of the protesters say they have been inspired by Wael Ghonim, a Google executive who has emerged as a prominent voice in a revolt galvanized in part by social networking sites. On Thursday, a Twitter feed in his name in English declared: “I promise every Egyptian that I will go back to my normal life & not be involved in any politics once Egyptians fulfill their dreams.”

But, in an interview on CNN, he was also quoted as saying he was “ready to die” for the opposition’s cause. “And I’m telling this to Omar Suleiman,” he said. “He’s going to watch this. You’re not going to stop us. Kidnap me, kidnap all my colleagues. Put us in jail. Kill us. Do whatever you want to do. We are getting back our country. You guys have been ruining this country for 30 years.”

The protests at Al Ahram by freelance reporters demanding better wages and more independence from the government snarled one of the state’s most powerful propaganda tools and seemed to change its tone: On Wednesday, the front page, which had sought for days to play down the protests, called recent attacks by pro-Mubarak protesters on Tahrir Square an “offense to the whole nation.”

And on Thursday, the newspaper’s online edition in English broke news of hotel closures in Sharm El-Sheikh, the heart of Egypt’s Red Sea tourism industry, which was badly hit when many visitors fled the country as the uprising broke out.

Outside Cairo’s main post office, about 100 people gathered to demand higher wages and more jobs as a series of stoppages percolated through the capital. “Everyone has begun demanding their rights,” said Ahmed Suleiman, 29, a part-time postal worker. “And it’s time for the government to meet them.” He spoke under a banner proclaiming: “Egyptian post office in solidarity with the youth of Tahrir Square.”

As the city braced for bigger protests that organizers are trying to muster for Friday — the Muslim holy day and the beginning of the weekend — the authorities appeared to have strung more razor wire around the state radio and television building towering over the Nile. The move seemed to reflect concern that protesters may try to move to new locations, expanding their presence.

On the diplomatic front, Mr. Aboul Gheit’s retort to Mr. Biden played into the complicated relationship between Mr. Mubarak’s government and the Obama administration, which had urged swift steps toward a political transition, then endorsed Mr. Mubarak’s remaining until the end of his term later this year. Since then, Mr. Biden has suggested that the United States still expects some immediate changes to be made.

On Wednesday, the White House press secretary, Robert Gibbs, responded to the Egyptian government’s claims that such changes were premature, saying, “What you see happening on the streets of Cairo is not all that surprising when you see the lack of steps that their government has taken to meet their concerns.”

That attempt to put some distance between the United States and Mr. Mubarak, though, was unlikely to impress the protesters, who say that the Obama administration, by continuing to back the president, also ignores their concerns.

By nightfall on Wednesday, more than 1,000 protesters prepared to sleep outside the Parliament building for a second night, a symbolic move that showed the opposition’s growing confidence as the protesters expanded the scope of their activism beyond Tahrir Square.

Reports from around the country of vigorous and sometimes violent protests also suggested a movement regaining steam.

Security officials said that five people died and more than 100 were injured during protests on Tuesday in El Kharga, 375 miles south of Cairo. Protesters responded Wednesday by burning police stations and other government buildings. In Asyut, protesters blocked a railway line. Television images showed crowds gathering again in Alexandria, Egypt’s second-largest city.

Even protests that were not directly against Mr. Mubarak centered on the types of government neglect that have driven the call for him to leave power.

Protesters in Port Said, a city of 600,000 at the mouth of the Suez Canal, set fire to a government building, saying local officials had ignored their requests for better housing. And in one of the most potentially significant labor actions, thousands of workers for the Suez Canal Authority continued a sit-in on Wednesday, though there were no immediate suggestions of disruptions of shipping in the canal, a vital international waterway.

On Wednesday, Human Rights Watch reported that since Jan. 28, when troops took up positions in Egyptian cities, army officers and the military police had arbitrarily detained at least 119 people. In at least five cases, the group said, detainees said they had been tortured.

There were signs that the police, under the jurisdiction of the hated Interior Ministry, were trying to remake their image. The authorities have announced in recent days that prosecutors are weighing charges against Habib el-Adly, recently removed as interior minister. The charges, including murder, are related to the killing of protesters by security officers during the unrest.

On Wednesday, some cellphone customers in Egypt received the equivalent of marketing messages from the new minister, Mahmoud Wagdy. One read, “From the Ministry of Interior: The police will do nothing but serve and protect the people.” Another said, “Starting today, we will only deal through truthfulness, honesty and rule of law.”

As Mr. Mubarak held on to power, influential groups and people seemed determined to distance themselves from his government’s legacy. Members of a prominent journalists’ association moved toward a no-confidence vote against their leader, Makram Mohamed Ahmed, a former Mubarak speechwriter, the daily Al Masry Al Youm reported on its English-language Web site.

And the recently appointed culture minister, Gaber Asfour, a literary critic, resigned Wednesday after pressure from his colleagues, according to Al Ahram.

Outside groups, meanwhile, continued to try to take advantage of the Egyptian uprising. In an online forum, a group in Iraq affiliated with Al Qaeda called on Egyptians to “wage violent jihad to topple the regime in Egypt,” according to Khaled Hamza, the editor of the Web site of the Muslim Brotherhood, Egypt’s largest opposition movement.

He bristled at the comments, saying the revolt in Egypt was nonviolent and included “all sects, trends and religions.”

“Egyptians are capable of solving their problem without intrusion, meddling and prying from foreign groups such as Al Qaeda and similar groups advocating the use of violence,” he said.

Increasingly, the political clamor for Mr. Mubarak’s ouster seemed to be complemented by strikes nationwide. While many strikes seemed to focus on specific grievances related to working conditions, labor leaders suggested they were energized by protests against Mr. Mubarak.

The protest against the Suez Canal Authority began Tuesday night and was staged by about 6,000 workers. In Helwan, 6,000 workers at the Misr Helwan Spinning and Weaving Company went on strike, Ms. Refaat said.

More than 2,000 workers from the Sigma pharmaceutical company in Quesna began a strike while about 5,000 unemployed youths stormed a government building in Aswan, demanding the dismissal of the governor.

In Cairo, sanitation workers demonstrated outside their headquarters.