CAIRO — Two Egyptian leaders have been struck down in 30 years: one by an Islamist assassin's bullets, the other by the demands of hundreds of thousands of protesters in a peaceful uprising. The first event, the death of President Anwar Sadat, marked a spectacle of the most militant brand of political Islam. The revolution the world witnessed Friday, the toppling of President Hosni Mubarak, may herald the dawn of something else.

There is a fear in the West, one rarely echoed here, that Egypt's revolution could go the way of Iran's, when radical Islamists ultimately commandeered a movement that began with a far broader base. But the two are very different countries. In Egypt, the uprising offers the possibility of an accommodation with political Islam rare in the Arab world — that without the repression that accompanied Mubarak's rule, Islam could present itself in a more moderate guise.

Egypt's was a revolution of diversity, a proliferation of voices — of youth, women, and workers as well as the religious — all of which will struggle for influence. Here, political Islam will most likely face a new kind of challenge: proving its relevance and popularity in a country undergoing seismic change.

''Choosing a regime will become the right of the people," Ali Abdel-Fattah, a Muslim Brotherhood leader, said Saturday. "The nature of the regime will be decided by elections. And I think Egyptians agree on the demands and how to realize them."

Of countries in the region, only Turkey has managed to incorporate currents of political Islam into a system that has so far proven viable, but its bold experiment remains unfinished. The rest of the region is strewn with disasters, from the ascent of the most militant strands in Iraq after the American invasion to the rise of populist and combative movements in the Palestinian territories and Lebanon that emerged under Israeli occupation.

In Egypt, repression of its Islamic activists helped give rise to the most extremist forces in the Muslim world — leadership of al-Qaida in Afghanistan and an insurgency against its own government in the 1990s.

But at its core the revolt that finally toppled Mubarak had a very different set of demands. Its organizers rallied to broad calls for freedom, social justice and a vague sense of nationalism that coalesced around a demand that distant and often incompetent rulers had to treat them with respect. They were voiced by youth, women, workers and adherents of revived currents of liberalism, the left and Arab nationalism, spread by social networks made possible by new technology.

The Muslim Brotherhood, a mainstream group that stands as the most venerable of the Arab world's Islamic movements, is of course also a contender to lead a new Egypt. It has long been the most organized and credible opposition to Mubarak. But it also must prepare to enter the fray of an emerging democratic system, testing its staying power in a system ruled by elections and the law.

''This is not yesterday's Egypt," declared Amal Borham, a protester in the square.

''It is their right to participate as much as it is mine, as much as it is anyone else's in this country," added Borham, who considers herself secular. "They are part of this society, and they have been made to stay in the shadows for a very long time."

The protests illustrated the challenges before the Brotherhood and other Islamic groups. While the Brotherhood eventually brought its organizational prowess to the demonstrations — organizing security and deploying its followers overnight, when the protests lulled — it was reluctant to join at first. Indeed, many protesters saw it as a representative of an old guard that they believed had for so long failed to answer society's problems.

Even some of the Brotherhood's own youthful supporters expressed frustration with their leaders' cautiousness.

''On Tuesday they were not convinced," recalled Islam Lotfi, a 32-year-old organizer and leader of the Brotherhood's youth. "On Wednesday, it was 'maybe.' And on Thursday, 'It seems you did a great job. Go ahead and this time we will follow.'"

It will undoubtedly moderate its message in a campaign, attempting to appeal to the broadest constituency. The next elections promise to be far more competitive than the shams of past years when many Egyptians simply stayed home. That emerging diversity may prove more uncomfortable than the head-to-head confrontation with Mubarak's enforcers that helped define its appeal.

''The system made them work in the dark and that made them look bigger than they are," said Ahmed Gowhary, a secular organizer of the protests. "Now it will be a real chance for them to show that they are more Egyptian than they have appeared."

''Their real power," he added, "will show."

The Arab world has a spectrum of Islamic movements, as broad as the states that have repressed them, from the most violent in al-Qaida to the most mainstream in Turkey. Though cast for years as an insurgent threat by Mubarak, the Brotherhood in Egypt has long disavowed its violent past, and now has a chance to present itself as something more than a force for opposition to Mubarak's authoritarianism.

Founded by a schoolteacher named Hassan el-Banna in the Suez Canal town of Ismailiyya in 1928, it quickly became the most important political contestant in the country, boasting a vibrant press, delivering weekly lectures from mosques and reaching out to students, civil servants, urban laborers and peasants. It was banned in 1954 under Gamal Abdel Nasser, the founder of Mubarak's state, weathering a brutal crackdown that instilled it in the iron discipline of a clandestine movement.

The repression, which persisted until last month, produced some of the Muslim world's most militant thinkers, Sayyid Qutb among them, who had a profound impact on militancy across the Muslim world. But remarkably, the movement also evolved over those same years, pursuing coalitions with other political parties since 1984, joining street protests with leftist groups and entering a feeble Parliament as independents, whose demands were not enforcement of Islamic strictures but opposition to martial law.

Its former leader turned heads in 2005 when he offered a play on the group's traditional slogan, "Islam is the solution." ''Freedom is the solution," he declared.

The Brotherhood's relationship with the government came full circle last Sunday, when Vice President Omar Suleiman invited it to talks. The discussions were meaningless, but the symbolism was vast: Only one seat separated the Brotherhood's spokesman from a man whose intelligence apparatus long deemed the group as the greatest threat to its rule.

''It exposed the lie of the regime that the Brotherhood is a violent organization, anti-systemic and a threat to the country," said Samer Shehata, a professor at Georgetown University.

Although Iran's and Egypt's revolutions share a date, Feb. 11, the fleeting comparisons end there. Millions welcomed Ayatollah Ruhollah Khomeini on his return from Paris. In Egypt, there was no charismatic figure of stature.

Unlike the Shiite Muslim clergy in Iran, the Muslim Brotherhood is neither led by clerics nor based on a clerical organization. In many ways, it represents a lay middle class. The very dynamics are different, too: cassette tapes of Ayatollah Khomeini's speeches helped drive Iran's revolution, whose zealots sought to export it. The Internet helped propel the uprisings in Egypt and Tunisia, the medium's own diffusion helping carry it from the backwater town of Sidi Bouzid in Tunisia to Tahrir Square in Cairo.

Perhaps most importantly, the revolutions occurred a generation apart, a note echoed in the Brotherhood stronghold of Munira, along streets of graceful balustrades of the colonial era and the utilitarian architecture of Nasser and his successors.

''The people are aware this time," said Essam Salem, a 50-year-old resident there. "They're not going to let them seize power. People aren't going to be deceived again. This is a popular revolution, a revolution of the youth, not an Islamic revolution."

In the struggle, morality was rarely mentioned, even by the Muslim Brotherhood, which echoed the demands that swung broad segments of Egypt's population to the revolution's side.

''We're a part of the people and there is a consensus over the people's demands," said Hamdi Hassan, another Brotherhood official.

Across the Arab world, the most militant Islamic movements are those embedded in conflict — Hezbollah and Hamas — or stateless, like al-Qaida, celebrating in mystical terms this generation's equivalent of armed struggle. Iraq's bloodiest spectacles, claimed by a homegrown Islamic militant movement, occurred in a civil war that followed the American invasion.

Comment on this story

In many ways, the Brotherhood is the counterexample, echoed in the success of Turkey's Justice and Development Party. It has de-emphasized the mainstays of Islamic activism — charity and proselytizing, for instance — for the prize of political success in Parliament.

While it remains deeply conservative, it engages less in sometimes frivolous debates over the veil or education and more in demands articulated by the broader society: corruption, joblessness, political freedom and human rights abuses.

The shift illustrates both its strengths and its weaknesses.

''The ability to present a mainstream national reform agenda and mobilize and galvanize Egyptians around this agenda, this is something the Muslim Brotherhood has failed to do," said Emad Shaheen, a professor at the University of Notre Dame. "The youth have achieved in 18 days what the Brotherhood failed to achieve in 80 years."