Al Qaeda is widely seen as weak in Egypt thanks partly to Mubarak, and his departure is raising fears in the U.S. Congress that the rise of even moderate Islamists may give radical elements more room to operate.

James Clapper, the U.S. director of national intelligence, sought to play down fears about the Muslim Brotherhood this week, saying it "has eschewed violence and has decried al Qaeda as a perversion of Islam."

"They have pursued social ends, betterment of the political order in Egypt, et cetera," he told lawmakers on Thursday.

Clapper acknowledged that the Muslim Brotherhood was only an umbrella group, and FBI Director Robert Mueller noted that some elements have supported terrorism in the past.

The movement, which Mubarak's government banned and sought to demonize, is certainly hostile to Israel and the U.S. policy in the region.

It has historic links with the Palestinian Islamist movement Hamas, which Washington considers to be a terrorist organization, and shares its belief in armed struggle against Israel.

But unlike the militant groups that fought Mubarak's rule in the 1990s, the Brotherhood is led by professionals with modern educations -- engineers, doctors, lawyers and academics. The core membership is middle-class or lower middle-class.

President Barack Obama himself has acknowledged the group's anti-American ideological strains but said the Muslim Brotherhood did not have majority support in Egypt.

The group itself said on Saturday it would not seek a parliamentary majority or the presidency.

FRAYED NERVES

But that is unlikely to sooth frayed nerves in the U.S. Congress, where anxiety is growing that Islamic extremists might turn a key U.S. ally into an opponent that would harbor militant groups and pose a threat to Israel.

Representative Ileana Ros-Lehtinen, the Republican chairwoman of the House of Representatives Foreign Affairs Committee, warned against allowing the Muslim Brotherhood to emerge as a powerful force.

Representative Sue Myrick, also a Republican, called them a danger to post-Mubarak Egypt.

"The Brotherhood isn't a danger just because they're terrorists, but because they push an extremist ideology that causes others to commit acts of terrorism," Myrick said.

U.S. intelligence officials say al Qaeda, despite thriving in nearby states like Yemen and Somalia, is not currently seen as a serious threat in Egypt.

A senior U.S. defense official, speaking on condition of anonymity, said al Qaeda's leaders likely view events in Egypt as positive steps toward Islamic radicalism but doubted they would be able to quickly exploit the power vacuum.

"Rather than democracy triumphing, they see this as the first stage that sets the conditions for them. Think Russian revolution," the official said, speaking before Mubarak's ousting, without personally taking that position.

Instead, U.S. officials say they believe the pro-democracy movement in Egypt may puncture the al Qaeda narrative that violence is needed to bring change.

"With respect to what's going on in Egypt, I think this truly a tectonic event," Clapper said on Thursday.

"There (is) potentially a great opportunity here to come up with a counter-narrative to al Qaeda."