Amr Moussa, a front-runner for Egypt's presidency, said on Sunday the strong Islamist showing in the first parliamentary election since army generals replaced Hosni Mubarak in February had to be swallowed as democracy in action.

The Muslim Brotherhood has also urged its rivals to accept the will of the people after a first-round vote set its party on course to take the most seats in parliament, with a hardline Salafi Islamist party thrusting liberals into third place.

Overall election results suggest Islamist parties, while not united, may wield a two-thirds majority in parliament.

In line with the Brotherhood's pragmatic image, the group's Freedom and Justice party may avoid lining up with its ultra-conservative Islamist rivals.

But its popular mandate will strengthen its hand in any power struggle with the military over Egypt's political future.

Egyptians return to the polls on Monday for 52 run-off votes for individual candidates, who will occupy a third of the 498 elected seats in the lower house once two more rounds of the complicated voting process end in January. Two-thirds of the seats are allocated proportionately to party lists.

Figures released by the election committee and published by state media show a list led by the Brotherhood's FJP securing 36.6 percent of valid party-list votes, followed by the Salafi al-Nour Party with 24.4 percent, and the liberal Egyptian Bloc with 13.4 percent.

The liberal Wafd Party took 7.1 percent, the moderate Islamist Wasat Party 4.3 percent, while the Revolution Continues, a group formed by youth activists, picked up 3.5 percent. The rest went to smaller party lists.

I am happy about the application of the democratic process, the beginning of democracy, said Moussa, a former Mubarak-era foreign minister and secretary-general of the Arab League.

You cannot have democracy and then amend or reject the results, he told Reuters by telephone, adding that the shape of parliament would not be clear until the voting was over.

ALARM IN ISRAEL

Israel's Defence Minister Ehud Barak described the Islamist success in the first Arab nation to recognise the Jewish state and to sign a peace treaty with it as very, very worrisome.

It is too early to predict how the changes that we face will end up. It could be that in a historical context, they are positive. In an immediate context, they are problematic, he told Israel's Channel Two television on Saturday.

The fate of the 1979 treaty between Egypt and Israel is also a concern for its sponsor, the United States, which has backed it with billions of dollars in military aid for both countries.

The Muslim Brotherhood, spiritual father of the Islamist Palestinian Hamas group, shares widespread Arab hostility to Israel, but it has not called for revoking the treaty.

Moussa, 75, an urbane and affable diplomat-turned- politician, is popular with many Egyptians for his nationalism and his perceived independence from Mubarak during his decade at the helm of the Arab League, where he stepped down in June.

With the apparent gains about the Islamic trend, let us see, he said. This will fall on the other forces, the liberal forces, to get together and form a strong front in parliament.

The assembly's popular mandate will give it clout to stand up to the generals who have ruled Egypt for nine turbulent months since a popular uprising toppled Mubarak on February 11.

TUSSLE OVER CONSTITUTION

The Brotherhood, Egypt's best-organised political group and popular with the poor for its decades of charity work, was banned but semi-tolerated under Mubarak. It now wants to shape a new constitution to be drawn up next year.

That could be the focus of a power struggle with the ruling military council, which wants to keep a presidential system, rather than the parliamentary one favoured by the Brotherhood.

I believe the constitutional debate will be a very serious and tough one. I don't think any party can impose its own language or principles, Moussa said. The constitution will have to be the outcome of consensus and general debate among the people. The liberal camp is also strong.

The Salafis are expected to demand that purist Islamist codes be reflected in the constitution and other legislation, forcing the Brotherhood to defend its own Islamist image.

The Salafis are certainly going to insert religion and identity into the political discourse like never before, said Shadi Hamid, director of research at the Brookings Doha Center.

The Brotherhood is going to come under pressure from the right. It runs the risk of losing supporters to the Salafis if it is not seen to be authentically Islamist enough.

The constitution, to be written by a constituent assembly chosen by parliament, may go to a referendum before a presidential election in June, under an accelerated timetable for a handover to civilian rule.

The generals, who had envisaged keeping power until end-2012 or beyond, agreed to a speedier transfer after last month's bloody street protests against army rule killed 42 people.

The man they appointed to lead a new interim cabinet was quoted on Saturday as saying he would not name his ministerial line-up until Wednesday, in the latest of several delays.

Kamal al-Ganzouri, told the state-owned al-Ahram newspaper he did not want to appoint a new interior minister to oversee law and order on the eve of Monday's run-off votes.

(Additional reporting by Maha El Dayan, Tom Pfeiffer and Tamim Elyan; Writing by Alistair Lyon)