Foreign ministers from Saudi Arabia and Kuwait met with the commander of the Lebanese ychristian militia for three hours today in an unexpected development that raised cautious hopes of a breakthrough in this country's factional fighting.

Militia leader Bechir Gemayel said after the talks, "I hope this initiative will make it possible to solve the crisis," But he warned that it was "too early to say success or failure" would come from the effort.

One firm demand made by the two foreign ministers, according to several sources, was that the Lebanese Christians sever their ties with Israel, a condition that Syria has frequently stated must be met before there can be any resolution of the Middle East missile crisis, which grew out of the factional fighting.

The meeting with Gamayel came after scheduled talks among the foreign ministers of Saudi Arabia, Kuwait and Syria and Lebanese officials. The group forms an Arab League committee that is attempting to negotiate an end to fighting in Lebanon, a step that is considered crucial to U.S. envoy Philip C. Habib's effort to resolve the Syrian-Israeli dispute over the presence of Syrian antiaircraft missiles in Lebanon.

Habib remained in Paris today, but a U.S. Embassy spokesman there said he would resume his diplomatic mission in the Middle East Monday.

The current 10-week round of fighting in Lebanon, with Syrian peacekeeping forces and Lebanese leftists and Moslems on one side and the Christians on the other, has killed an estimated 750 persons.

Gemayel's meeting with Saudi Foreign Minister Saud Faisal and Kuwaiti Foreign Minister Sabah Ahmad Sabah stole the limelight from the formal conference this morning in this hill town 25 miles southeast of Beirut. f

Together with similar meetings with other Lebanese politicians and warlords, the encounter was designed to associate the real power brokers with any decision in the hopes of winning at least temporary respite from Lebanon's years of civil strife.

Summing up the meetings with Moslem and Christian leaders, Sabah said he and his Saudi colleague "felt all sides have been responsive."

Moslem politicians echoed Gemayel's pledge to cooperate with the Arab ministers "to the fullest extent" but warned that no solutions had been reached.

The Christian Phalangist Radio said the Arab foreign ministers discussed a cease-fire, withdrawal of heavy weapons, presumably from urban areas, and formation of a committee to oversee this divided country's precarious security.

That committee, with Arab ambassadors here serving as members, would then discuss the makeup of the now totally Syrian 22,000-member Arab Deterrent Force sent here at the end of the 1975-76 civil war.

The Christians have demanded that the Arab Deterrent Force be expanded to include Saudis, Kuwaitis and other Arabs who once had contingents on the force. ysome sources indicated, however, that the presence of observer officers from these states might meet these demands.

Similar plans in the past have had no success. But this time Habib has sought to involve the Saudis and Kuwaitis, who threw up their hands over Lebanon in 1978, in moves to ease the missile dispute.

Another formal conference session was scheduled for Monday, before Syrian Foreign Minister Abdul Halim Khaddam and his Kuwaiti and Saudi colleagues are expected to leave for home.

With Habib's mission hanging on the outcome of the Arab League undertaking, the Kuwaiti and Saudi ministers went out of their way to flatter the Christian commander.

Gemayel was received before other Lebanese leaders including his father, Pierre Gemayel, who is the titular head of the Phalangist Party, which constitutes the core of the Christian militias.

But various political sources claiming to be privy to the talks said Saudi Arabia and Kuwait -- often seen as U.S. surrogates in the Middle East political lineup -- were as firm as Syria in demanding that the militias break their ties with Israel.

Bechir Gemayel did not specifically mention these demands -- which were echoed by a Damascus Radio broadcast demanding the links be "severed immediately and without delay" -- but appeared to allude to them in noting that "certain issues require, deep thinking."

Militia sources indicated they would require formal guarantees from Saudi Arabia and Kuwait -- and in their eyes that meant U.S. backing as well -- before cutting links with Israel.