WASHINGTON - No sooner had Egyptian President Hosni Mubarak stepped down on Friday than the chairwoman of the US House Foreign Affairs Committee warned against letting the Muslim Brotherhood emerge as a powerful force. The comments by Republican Representative Ileana Ros-Lehtinen reflect anxiety in Congress that Islamist extremists might turn a key US ally into an opponent that would harbor militant groups bent on harming America and tearing up Cairo's peace deal with Israel. "We must also urge the unequivocal rejection of any involvement by the Muslim Brotherhood and other extremists who may seek to exploit and hijack these events to gain power, oppress the Egyptian people, and do great harm to Egypt's relationship with the United States, Israel, and other free nations," Ros-Lehtinen said in a statement. She said the United States must focus on helping create conditions for a "calm and orderly transition process toward freedom and democracy in Egypt." Other US lawmakers did not explicitly warn against the Muslim Brotherhood, which Mubarak's government had banned and demonized as seeking to install a Sunni theocracy. But many in Congress expressed concerns about what may be coming next in Egypt, saying they hope an Iranian-style Islamist revolution will not follow the current turmoil. "I do not believe the people of Egypt have undertaken this glorious, peaceful revolution in order to substitute a repressive religious regime and regional instability for the stifling and brutal Mubarak regime," said Gary Ackerman, the top Democrat on the House Middle East subcommittee. "I am concerned about an orderly transition to what? Or an orderly transition to who?" Representative Mike Pence, a Republican, said during a hearing of Ros-Lehtinen's committee on Thursday, the day before Mubarak stepped down. Some analysts think worries about the Muslim Brotherhood are overblown. The group is seen as Egypt's largest opposition group but took a backseat in the early part of the protests. Its previous strategy had been to win over Egypt's majority Muslim population gradually to its vision of a pluralistic, democratic and Islamist state. The group once had secret paramilitary arm but now says it is committed to democratic means. While hostile to Israel and US policy in the region, the Brotherhood has an overwhelmingly lay leadership of professionals with modern educations - engineers, doctors, lawyers, academics and teachers. The core membership is middle-class or lower middle-class. Qamar-ul Huda, a Middle East expert at the United States Institute for Peace think tank, dismissed concerns that Mubarak's departure would clear the way for the Muslim Brotherhood's rise. "It has been blown out of proportion," he said. "There is a hysteria of making the worst-case scenario the only reality. I think civil society in Egypt will produce some sophisticated individuals to lead their parties."