It was the typical sort of soft jihad practiced by thousands of young men enrolled in the Muslim Brotherhood, Egypt's main Islamic political organization and largest opposition group. Abdel Rahman Essam collected money from students and adults for dialysis machines needed in hospitals and took the greetings and thank-yous of kidney patients and the healthy alike.

But as the Brotherhood field leader and medical student made his rounds at Alexandria University, he also heard pointed criticism. How was it, he was asked, that the Muslim Brotherhood stood on the sidelines of pro-democracy demonstrations in Alexandria, Cairo and other Egyptian cities against President Hosni Mubarak and his 24-year rule?

"I, too, was excited by the demonstrations," Essam said in an interview the other day on Alexandria's Mediterranean seafront. "Things were changing in Egypt. People found the moral courage to stand up. We love Egypt and are part of it, and we had to take part."

So he and like-minded young men across the country challenged their superiors. Their calls for action prompted the high command in the self-styled "guidance committee" to change course, Brotherhood leaders say. In late March, members of the Brotherhood began taking to the streets by the thousands to demand an end to laws that prohibit public gatherings and restrict membership in unauthorized political movements -- the Brotherhood being the biggest among them.

Since then, the Brotherhood has held more than a dozen demonstrations in several Egyptian cities. Participation has dwarfed the turnout at similar protests held by Kifaya, or Enough, the coalition of human rights, professional and legal organizations that began a drive to unseat Mubarak last fall. In response, the government arrested hundreds of Brotherhood activists -- from low-ranking members to higher-ups, including Essam Erian, a well-known spokesman, and Mahmoud Ezzat, one of the group's top Cairo operatives.

"The Brotherhood understood it could not keep its distance. The danger now for the Brotherhood is that, if it looks like a real alternative, the government will try to crush it," said Emad Din Shahin, a professor at the American University in Cairo.

The Brotherhood's shift in tactics contributed a new and powerful element to the struggle to unseat Mubarak and usher in competitive electoral democracy and freedom of speech, assembly and association. Among opposition groups, only the Brotherhood has the capacity to mobilize hundreds of thousands of protesters. It has demonstrated that strength in the past few years with protests against Israel's treatment of Palestinians and the U.S.-led war in Iraq.

Brotherhood influence extends beyond Egypt. At 77 years old (the same age as Mubarak), the Brotherhood is the model for Islamic organizations in Syria, Jordan and Sudan, and among the Palestinians. While it has renounced violence at home since the 1970s, the Brotherhood endorses resistance to "occupation" by groups such as the Palestinian organization Hamas, which in recent years has conducted a campaign of suicide bombings against Israelis.

For the Bush administration, which has called on Egypt to hold "fair and free" elections, the Brotherhood theoretically represents a viable partner in what the president has called a "march of democracy."

But support for Hamas makes the Brotherhood a problem in the administration's view -- even though Hamas, designated a terrorist organization by the State Department and known formally as the Islamic Resistance Movement, competes in Palestinian elections.

The Muslim Brotherhood has been banned from political activity in Egypt since 1954, after two decades of tumultuous activity that included assassination of its enemies. Brotherhood members, listed as independents, hold 17 seats in parliament, but that is a tiny share in the 484-member body. Mubarak's National Democratic Party occupies all but a handful of the other seats.

Analysts say the Brotherhood reached a turning point in March 2004, when it issued a list of 13 reform initiatives that, among other things, committed it to a parliamentary and democratic Egypt. The document referred to the people as the source of sovereignty -- a major philosophical switch. Strictly speaking, in the Brotherhood's view, God is the sole source of authority. "Political reform in the region cannot be effective and credible without the integration of moderate Islamists," Shahin said.

Ali Abdul Fattah, a senior Brotherhood official, said in an interview that the West cannot preach democracy and shut the door on Islamic politics. "You can't have democracy in Egypt without including us," he said.

Nonetheless, under election rules just passed in a referendum, independents are barred from the upcoming presidential race, effectively excluding any Brotherhood candidate.

On May 27 in Alexandria, Abdul Fattah organized a Brotherhood protest against the alleged desecration of the Koran by U.S. troops. It was part prayer meeting, part demonstration. About 5,000 protesters filed past rows of riot police and entered a seashore club belonging to the Lawyers' Syndicate, one of a number of government-sanctioned organizations to which Brotherhood members belong -- and which they sometimes dominate. Women dressed in long head scarves and longer caftans filed into separate quarters.

A preacher criticized Mubarak for remaining silent on the alleged desecrations. He lambasted the police for blocking the path of worshipers who streamed toward the club. "No to the America that insulted the Koran! America and the Jews, the enemies of God!" the crowd roared. A phalanx of protesters, holding aloft copies of the Koran, turned toward riot police on the waterfront drive. The police, wearing helmets with leather skirts draped down their necks for added protection, looked like sphinxes in black.

Among the Koran wavers were Abdel Rahman Essam and his comrade, Mohammed Rafik, a recent university graduate and medical equipment technician. The friends share the look and lifestyle of Brotherhood youth. They wear close-cut hair and crisply pressed clothing -- no backward baseball caps or low-slung jeans for them. They study and work hard, avoid the homegrown temptations of Egypt's throbbing shaabi music and dance, and regard Islam as the supreme guide for everything from marriage to relations with non-Muslims to, of course, managing Egypt.

Yet unlike the speech of many of their elders, their rhetoric oscillates between Islamic cant and secular nationalist cheerleading. They say things on the street that in the mosque would make beards curl. "We're all sons of the pharaoh," said Essam, 23, in a moment of solidarity with the goals of secular demonstrators.

"We need a chance to show we love Egypt and to make it better," said Rafik, 25. "Going into the streets is not really a decision, it's where we need to be. We should all get beaten together, if that is what is necessary. We even invite the National Democratic Party to join us."

Essam jokingly said he "inherited" his membership -- his father was a Brotherhood adept and his uncle was jailed for his activities. Rafik's parents were never members, but they approve of his role.

Both young men began their Brotherhood activities at the university, holding informal talks with students to explain the organization. Young recruits begin as officially designated "sympathizers," move to the level of "collaborator" and then to an internship, in which they perform services for the Brotherhood such as spreading propaganda, finding recruits or sweeping streets on one of their neighborhood cleanup drives.

Essam writes articles for Brotherhood publications; Rafik gives explanatory mini-lectures. Before moving up to higher levels of membership, they must attend secret training sessions in doctrine and practice. The training is the underground part of the Brotherhood; locations and topics are kept confidential.

"Islam provides everything you need to know -- the basis for science, everything," Essam said. He repeated the mythic view of Muslim history, which holds that Islam's medieval golden age was doomed by departure from religious principles. "We need to return to Islam, the way it was when we were giving knowledge to the whole world."

As the protest continued, the crowd chanted, "Islam is our constitution." It's the kind of statement that gives secular activists and potential allies pause. Kifaya, for instance, along with presidential candidate Ayman Nour, regards the Egyptian constitution -- not the Koran -- as the constitution, though they say it must be amended to limit presidential terms of office and open the way to competition for power.

Essam tried to explain. "Of course, this is 'Defend the Koran Day of Rage,' so we are talking a lot about the Koran. But we are in favor of letting the people choose. They want democracy, let them choose. They want the Koran, let them choose," he said.

He began to give the kind of lecture he says he delivers to doubters at the university. "Take a machine. Machines follow certain principles, but to fix them, you must be pragmatic. Islam does not reject reality. It deals with it."

Talk of compromise and reform has long made the Muslim Brotherhood a target of criticism by groups less prone to striking deals. In his 1991 book, "The Bitter Harvest," Ayman Zawahiri, an Egyptian and one of Osama bin Laden's deputies, launched a bitter attack on the Brotherhood. Reports that al Qaeda had set off bombs in Egyptian Red Sea resorts last fall raised the possibility that such terrorist groups would try to transport violent jihad into Egypt.

"We are against using violence to change Egypt. It is not the way," Essam said. "When Islam rules the world, you will see how we deal with people, and it will not be by force. Even with the Americans!"

Egyptian police, left, watch over Muslim Brotherhood protesters outside a mosque during a rally in Cairo on May 4.