The leaders of Lebanon's three main warring militias signed a Syrian-brokered accord in Damascus today to end 10 years of civil war that has ravaged their country and left more than 100,000 persons dead.

Details of the accord, which was signed at the office of Syrian Vice President Abdul Halim Khaddam, were not released. The signatories to the accord were the leader of the Druze militia Walid Jumblatt, the head of the Shiite Moslem militia Amal, Nabih Berri, and the chief of the dominant Christian militia known as the Lebanese Forces, Elie Hobeika.

The meeting was the first face-to-face encounter involving Moslem militia leaders Jumblatt and Berri as well as Hobeika, who took over the leadership of the Lebanese Forces after the militia split from the Phalangist Party of Lebanese President Amin Gemayel in March.

The agreement, which formally ends the state of war among Lebanon's feuding militias, was believed to include radical political changes that would alter Lebanon's sectarian power-sharing system by giving the country's Moslem majority a bigger role in government and reducing the powers of the Christian-held presidency.

There also were provisions to ensure the country's security, including sending the Army to the barracks for "rehabilitation" and turning over enforcement tasks to the country's Internal Security Forces.

However, the terms of the agreement, which Syrian painstakingly mediated for three months, remained open to speculation in the absence of a published text.

A transitional period during which the current power-sharing system would remain in force was to ensue before the agreement's provisions could be implemented fully, said Michael Samaha, a key negotiator for the Lebanese Forces. A "national unity government" would be formed, Samaha told reporters before the signing ceremony.

Under the current political system, which is a result of a pact reached following the 1958 civil war rather than a constitutional amendment, Lebanon's Christians, who formed 45 percent of the population, enjoy a slight legislative majority.

One problem relating to holding general elections was whether it would be possible to hold them in the areas of southern Lebanon that are still dominated by Israel and the Israeli-backed Christian militia known as the South Lebanon Army, Samaha added.

Following the signing ceremony, which was preceded by four hours of discussion at Khaddam's office, Berri told reporters as he was heading for his car, "This is the agreement. I hope we can execute it. What is important is the application of this accord."

Jumblatt said he hoped Lebanon would not return to "the language of exchange shelling because this is not the language that will bring us solutions for an Arab democratic Lebanon."

But the mechanism for implementing the terms of the agreement were still being worked out by the three militia leaders, who met to draw up an implementation plan following the signing of the accord. A further meeting was scheduled for Sunday.

The prospects of the agreement's success were also uncertain because of the absence of several key political Lebanese figures. President Gemayel was not represented at the meeting, nor was the Sunni Moslem Prime Minister Rashid Karami. Two former Christian presidents, Camille Chamoun and Elias Franjieh, also did not attend.

Chamoun and Franjieh have voiced their opposition, shared by other hard-line Christians, to a redistribution of power that would limit the authority of the president, who must be a Christian Maronite under the Lebanese constitution, and give more power to the country's Moslems.