Followers of a puritanical form of Islam will fill about a quarter of the seats in the lower house of the new Egyptian parliament on Monday, underscoring the political power being wielded by Islamists in the wake of the Arab spring.

Finding themselves badly outnumbered, some Egyptian liberals are weighing whether to align themselves with the moderate Muslim Brotherhood in hopes of preventing an all-Islamist alliance between the Brotherhood, whose Freedom and Justice Party will be the largest in the new parliament, and the ultraconservative Salafist Nour party, the second-largest.

Some liberal Egyptian politicians say a tactical alliance between their forces and the Brotherhood is being encouraged by Western diplomats alarmed by the prospect of a further rightward shift after last year’s toppling of Hosni Mubarak. They say the two Islamist groups could be pushed together if liberals refuse to negotiate with the Muslim Brotherhood in the coming parliament, which will be tasked with appointing a body to write the constitution.

“They’re scared of the Salafis and they want the secular people to join with the Brotherhood so the Brotherhood and Salafis don’t join together,” Mohammed Abou el Ghar, who heads the leftist Social Democratic Party, said in describing what he called Western fears.

The Salafists adhere to a hard-line interpretation of Islam that advocates a staunch segregation of the sexes and forbids alcohol, and have insisted that they won't compromise their Islamic values. A history of rivalry between the two Islamist groups makes an alliance between the Salafists and the Muslim Brotherhood unlikely; the Nour Party’s precursor, the Salafist Call, was born from a movement founded in the 1970s to counter the Brotherhood’s domination at the university campus in Alexandria.

But the two parties do play to an overlapping Islamist base, and the Salafists’ strong electoral showing has given new prominence to issues involving morality. “The Nour Party’s presence definitely puts pressure on the Freedom and Justice Party” in a conservative direction, said Mohammed Beltagy, a Freedom and Justice parliament member, adding that his party’s own wins could pressure the Salafists to become more moderate.

While recent high-level American emissaries have reached out to the Muslim Brotherhood’s Freedom and Justice Party, U.S. officials have generally avoided the Nour Party. A first official meeting between U.S. Ambassador Anne Patterson and representatives of the Salafist Party has been scheduled for Sunday.

Members of the Salafist Party say they are trying to counter what they call a smear campaign trying to depict them as uncompromising and scary conservatives who will transform Egypt into a rigid Islamic state like Iran or Saudi Arabia.

They have stated publicly that they would conditionally respect the peace treaty between Egypt and Israel, and have tempered language about Islamic tourism and banking laws that scare foreign investors. The party has expressed interest in tacit agreements with liberals on social issues, such as striking the hated emergency law.

But members walk a fine line while trying to show they are willing to compromise and cooperate to the world and potential liberal partners while avoiding moves that could alienate their ultraconservative base. Nader Bakkar, a party spokesman, said the party does not intend to enter binding alliances with other political parties because it would compromise its Islamic principles.

“Often the liberal stream is very difficult to convince that we can find common ground on some points,” Bakkar said. “We are related to an ideology that is very clear, the Islamic ideology, but at the same time we are working for the best of our country and this is our common point.”

While public health and restarting the economy and services will be high on the agenda of the Nour Party, the institution of Islamic law is among its top priorities during the constitutional writing process, Bakkar said. He said the party favored the prohibition on the sale of alcohol to Muslims, though tourists would be permitted to bring it into the country and drink in hotel rooms. He said the party believed that women should be strongly encouraged to cover their hair in the Islamic tradition but would not be forced to do so.

Members have reached out to major liberal parties and figures, including the historic liberal party, Wafd, and the Free Egyptians, a secular party that has been most critical of the group. But the talks have so far failed to bloom, Nour Party members said, because liberals are hesitant to trust them.

Bakkar sat in the Indiana Hotel lobby in central Cairo this week where the Salafist parliamentarians were learning about economic and political theory in a seminar. Bearded men filled the lobby, a sight that would probably have prompted a crackdown by Mubarak’s security forces during his rule. The autocratic leader kept Islamists on a tight leash and Salafists in particular hid in the shadows for fear of retribution.

Any alliance between the Nour Party and liberals is considered unlikely, except on specific positions or to counter the Brotherhood power. Omar Ashour, an expert on Islamist movements at Exeter University, said liberals and Salafists would have very little in common — “except that they have a common enemy, the Muslim Brotherhood.’’