WASHINGTON – Egypt’s revolution, a secular popular revolt that used nonviolent means to humble an entrenched autocrat, will remake the Middle East — and could mark the end of the era that began on Sept. 11, 2001, according to U.S. officials, former officials and analysts here and in the Middle East.

If the Egyptian revolution delivers on its promise of a march toward democracy, the protesters in Tahrir Square will have dealt a stunning blow to al-Qaida and other radical groups, whose propagandists argue that their way — violence and a puritan form of Islam — are the only way to save the Muslim world.

If the most populous Arab state slips back into a new dictatorship or anarchy, however, extremists could find a fresh foothold and a new lease on life in an Arab population that polls show has largely rejected them.

The stakes for the U.S. in a region that has long bedeviled it are stratospheric.

“The Egyptian revolution could be a huge defeat or a huge victory for al-Qaida. It depends what happens,” said Kenneth Pollack, a former CIA and White House official who is now director of the Brookings Institution’s Saban Center for Middle East Policy. If things turn out well, “It could destroy their narrative,” he said.

CIA Director Leon Panetta told Congress on Thursday, before Mubarak’s departure was official, that the events in Egypt “will have tremendous impact. If it’s done right, it will help us a great deal in trying to promote stability in that part of the world. If it happens wrong, it could create some serious problems for us and for the rest of the world.”

In the short term, the exit of Egyptian President Hosni Mubarak, 82, puts new pressure on other long-sitting rulers to reform or meet a similar end.

While the ouster of governments first in Tunisia and then Egypt wasn’t predicted, analysts say that rulers in Arab republics — and particularly Algeria and Yemen — have more to fear than the hereditary monarchies in Jordan and the energy-rich Persian Gulf.

“Reform or revolution. Reform or rebellion. Reform or the entire regime can collapse,” said Shafeeq Ghabra, a political science professor at Kuwait University.

Ghabra said Mubarak’s removal will empower Arab nations’ bulging youth populations to speak out. He spoke by phone Friday from Morocco, where he said many were cheering Mubarak’s departure.

The pro-democracy movements are a “repudiation first and foremost of authoritarianism, of the leader functioning without sanction from the people. The former model” is what produced al-Qaida leaders Osama bin Laden and Ayman al-Zawahiri, said Nubar Hovsepian, an Egyptian-born political scientist at Chapman University, in Orange, Calif.

For the Obama administration’s Middle East policy, major change is in the offing, too. President Obama, who has emphasized Israeli-Palestinian peace talks and Iran’s nuclear program, will be forced to invest much more time and resources in democracy promotion and supporting Egypt’s uncertain transition.

Advocates say that Obama cut funding for democracy initiatives in Egypt and elsewhere and gave too little attention to the issue after delivering a major speech in Cairo early in his presidency.

“The question mark is now, are they going to get it?” Pollack said. “Let’s not wait until the next revolution” to push for democracy and openness, he said.

While the scenes from Cairo’s Tahrir Square were euphoric Friday, they seem likely to give way to more sober assessments of how Egypt can move to an open political system neither it nor most of its neighbors have ever known.

“There are risks,” Secretary of State Hillary Rodham Clinton said in a speech Sunday in Munich, Germany. “It can be chaotic. It can cause short-term instability. Even worse — and we have seen it before — the transition can backslide into just another authoritarian regime.”

Egypt itself was a midwife at the birth of al-Qaida and its ideology. The fundamentalist, anti-Western writings of Sayyid Qatb, hanged in Egypt in 1966, influenced later generations of Islamic radicals. Many of bin Laden’s top lieutenants, including al-Zawahiri, were Egyptian. Al-Zawahari merged his Egyptian Islamic Jihad group into al-Qaida in the 1990s.

Paul Pillar, who was the U.S. intelligence community’s top Middle East analyst until 2005, warned that Islamic extremist groups will seek to capitalize on any missteps or difficulties that Egypt and Tunisia encounter as they strive to implement the democratic reforms sought by the hundreds of thousands who took to the streets.

“There is no question that extremists will try to exploit the political flux in Egypt just as they would try to exploit them anywhere,” Pillar said. Still, he said, “I don’t see them very well positioned to do that organizationally or in terms of the message they peddle.”

Qamar-ul Huda, an expert on political Islam with the U.S. Institute for Peace, said that radical Islamic groups are very weak in Egypt, because Mubarak’s regime spent much of the 1990s ruthlessly suppressing them.

“That was Mubarak’s social contract: We will bring security, and in return we will ensure there will be food on the table and invest in infrastructure,” he said.

Mubarak and his cronies failed to uphold their end, monopolizing the business and financial sectors and accumulating vast fortunes as the majority of Egyptians endured poverty, unemployment, rising food prices and a denial of basic political and human rights, he said.

Surmounting those problems and improving daily life for most Egyptians and Tunisians could prove to be one of the toughest problems for the transitional authorities and the greatest opening for Islamic radicalism, experts agreed.