CAIRO - As they gathered in force for an 11th straight day, anti-government demonstrators spotted an unexpected face in their midst in Tahrir Square: Field Marshal Mohammed Hussein Tantawi, the Egyptian defense minister.

"The army and the people are united!" crowds shouted hopefully after his presence was announced Friday afternoon on a loudspeaker. Tantawi mingled with some of his troops and chatted with protesters, telling them that they had made their point and urging them to go home. But his presence underscored the degree to which both President Hosni Mubarak and the people calling for his head are counting on the country's military leadership to secure Egypt's political future, even if neither is sure where its loyalties will end up.

The 470,000-strong Egyptian military is far more than just a defense-related institution; like the Chinese military, it controls a wide array of factories, hotels and businesses, and its generals constitute a stratum of Egypt's elite.

"Egyptian military officers are in the upper echelon of society," said one former U.S. general with extensive experience in the Middle East and Egypt who spoke on the condition of anonymity to preserve his relationships in the region. "The biggest question for the Egyptian military is whether or not there will be a whole-scale change in the Egyptian elite, because the senior military officers are so much a part of that elite. . . . They may be indifferent on whether Mubarak stays or leaves."

But current and former U.S. officials described the Egyptian General Staff as fairly unified in its support of Mubarak. "If you are a general in the Egyptian army, you are beholden to Mubarak. You were handpicked by Mubarak," said a former U.S. military official who spoke on the condition of anonymity because he still consults with the Egyptian armed forces. "What you have is bureaucrats who were promoted because they were good managers and were loyal to Mubarak and Tantawi."

The 75-year-old Tantawi has long been derided by some Egyptian military officers as Mubarak's "poodle," and U.S. officials have expressed exasperation with Tantawi's firm resistance to change or reform of any sort.

In March 2008, a few days before Tantawi was scheduled to make a four-day visit to the United States, the U.S. Embassy in Cairo gave a blunt assessment of his abilities in a cable to the State Department.

"Washington interlocutors should be prepared to meet an aged and change-resistant Tantawi," read the cable, signed by then-Ambassador Francis J. Ricciardone and subsequently made public by the anti-secrecy Web site WikiLeaks. "He and Mubarak are focused on regime stability and maintaining the status quo through the end of their time. They simply do not have the energy, inclination or world view to do anything differently."

Last weekend, when Mubarak reshuffled his cabinet in a failed attempt to defuse the protests, he elevated his old ally to the rank of deputy prime minister.

Since then, Obama administration officials have assiduously urged Tantawi to avoid an army crackdown against the protesters. His counterpart at the Pentagon, Defense Secretary Robert M. Gates, has called him four times, most recently on Friday.

At the same time, other U.S. officials have repeatedly delivered the same message to Lt. Gen. Sami Enan, Egypt's chief of the armed forces, in the hopes that the military can gently maintain a measure of stability amid attempts to usher Mubarak out of office. The United States provides Egypt with about $1.3 billion in military aid each year.

U.S. officials say they are reluctant to cut off military aid right now, as some analysts and lawmakers have suggested, because they think the Egyptian military has mostly acted well and remained neutral in the conflict.

If Mubarak were forced from office, some Egypt analysts speculated that Enan would probably leave his post as well. "He is too close to Mubarak to stay," said Gawdat Bahgat, a professor at National Defense University in Washington who has worked extensively with Egyptian officers attending the school.

Some senior U.S. officials, however, view Enan as a trusted partner. Retired Army Lt. Gen. R. Steven Whitcomb, who oversaw joint exercises with the Egyptian military while stationed in the Middle East, invited Enan and his wife to his home at Fort McPherson in Atlanta for a private dinner in 2007. According to Whitcomb, Enan complained about the effect that budget cuts were having on the military as the Mubarak administration dealt with political and economic problems.

Despite the cuts, U.S. officials said that the Egyptian military continued to function well. "Their equipment was old, but pretty well maintained," Whitcomb said.

Others played down the roles of Enan and Tantawi as Egypt moves forward. "Enan is a figurehead. He really doesn't matter," said the former U.S. military official.

Egypt's modern history has been marked by a succession of military coups and strongman rule, beginning in 1952, when a group of young army officers led by Col. Gamal Abdel Nasser revolted against King Farouk and established the Arab Republic of Egypt.

Mubarak, a former air force general, has served as president since 1981. Although he has remained close to the armed forces, analysts said most Egyptian military leaders are steadfastly opposed to another coup or taking control of the government.

When Mubarak does leave - he has pledged to step down by September, although protesters want him to go now - a looming question is whether the largely secular Egyptian military can coexist with Islamist political parties that will seek to fill the vacuum. Mubarak and the military for decades have relentlessly repressed Islamist leaders, particularly figures from the Muslim Brotherhood, the movement that seeks to establish a government based on Islamic law.

The former U.S. general doubted that the Egyptian military would be able to work closely with a government dominated by the Muslim Brotherhood. "They have been fighting the Muslim Brotherhood since 1952," he said. "Sometimes they have tried to reach an accommodation with them. But it has never worked. There are deep scars between the two."

Despite this history of antagonism, analysts said that cooperation was not out of the question. "The Egyptian army will accept the Muslim Brotherhood because it has no other choice," said Bahgat, the National Defense University professor. "The Egyptian army is the best-organized institution in Egypt. The Muslim Brotherhood is the best-organized political group. They must work together."

Indeed, leaders of the Muslim Brotherhood have spoken favorably in recent days about Enan, saying they would support his taking a role on a "transition council" that would govern until elections can be held.

Emile Nakhleh, a former CIA analyst and an expert on Islamist movements, said the Muslim Brotherhood would much rather deal with the Egyptian military than the security services or intelligence agencies, which have taken an even harsher line against Islamists. He said the Brotherhood has been particularly opposed to Omar Suleiman, the former spy chief whom Mubarak elevated to vice president this week.

"They would like not only Mubarak to go, but Suleiman also," he said. "They view him as an extension of the regime."

Jaffe reported from Washington. Staff writer Mary Beth Sheridan and staff researcher Julie Tate contributed to this report.