The commander of Lebanon's Maronite Christian militia flew unexpectedly to Saudi Arabia today to meet with Arab League representatives who are seeking a solution to the Lebanese crisis.

Maronite Bashir Gemayel, who has long been unofficially allied with Israel, met with Saudi King Fahd and other high Arab officials in an apparent quest for Arab approval of his effort to become president of Lebanon. That position has limited power at the moment but has potentially greater significance if a satisfactory solution to the present crisis can be achieved.

Gemayel's surprise initiative came amid new Israeli demands for a speedy withdrawal of Palestinian guerrilla forces from the besieged Lebanese capital and continued U.S. efforts to negotiate an agreement.

Although the cease-fire continued in effect for a sixth day today, Israeli warplanes startled residents of West Beirut and the thousands of Palestine Liberation Organization guerrillas there before dawn when they dropped flares and smoke bombs in an apparent effort to put pressure on the PLO to accept Israel's demands.

Recent clashes in mountain villages between Christian Phalangist rightists and Moslem Druze militiamen brought an added complication to negotiations, Reuter reported early Friday.

Top PLO aide Salah Khalaf was quoted in a Beirut newspaper as saying that "the killing of our brothers, the Druze Moslems" by the Phalangists had made the PLO more determined to stick to its positions, Reuter said. Related story, Page A24.

Israel and the PLO, as well as the United States and the Lebanese government, reportedly have been in agreement in principle that the guerrillas will leave Beirut, but serious differences still remain on the disposition of their weapons and whether they can continue to maintain political and other offices after their forces leave.

Morris Draper, the U.S. deputy assistant secretary of state for Middle East affairs who is assisting special envoy Philip C. Habib in negotiating toward an agreement, was dispatched from Beirut to Israel today to explain current developments here to Israeli Prime Minister Menachem Begin. But neither side gave details of Draper's report.

Similarly, no details were made public of the closed meeting in Taif, the Saudi summer capital, where foreign ministers and other representatives of Saudi Arabia, Syria, Kuwait, Algeria, Lebanon, the PLO and the Arab League met with Gemayel.

The group discussed a Saudi plan suggested as a way out of the deadlock over withdrawal of PLO forces from Beirut, an informed source in Saudi Arabia told The Washington Post.

According to this source, the three-point plan called for withdrawal of the PLO command and military forces except for about 1,000 Palestine Liberation Army troops that would be put under Lebanese command; similar Palestinian contingents to be distributed among Syrian, Jordanian and Egyptian armies; and a Lebanese guarantee of the safety of all Palestinians residing on Lebanese soil against any future acts of "atrocity, threat and aggression."

Gemayel left Beirut secretly for Cyprus by undisclosed means provided by the United States, according to his associates. From there a Saudi plane flew him to Taif.

Even by the standards of rapidly changing Middle East politics, the mission of 34-year-old Gemayel appeared a long-shot gamble.

For the militia leader, long unofficially allied with Israel, has been the Palestinians' most outspoken enemy since even before Lebanon's civil war broke out in April 1975 and plunged this country into an ever more brutal pattern of violence.

But analysts and politicians were convinced that it was for that very reason that Habib and the Saudis believed Gemayel represented the last, best chance to avoid the destruction of both West Beirut and the PLO. An Israeli invasion of the city to crush the Palestinian guerrillas would have serious repercussions for the United States and its moderate Arab allies.

A Gemayel lieutenant said the official invitation tendered with American blessing at 9:30 p.m. yesterday by Prince Saud Faisal, the Saudi foreign minister, constituted "Arab world consecration" for the militia commander--long suspect in Arab eyes for his Israeli ties and violently anti-Moslem actions during the civil war.

The Saudis have the money, influence and ability if they choose to help Gemayel achieve the Lebanese presidency, which constitutionally falls vacant later this month.

A Saudi stamp of approval--and Saudi oil money--could help wipe away the stigma of Gemayel's past and deliver the Moslem votes he needs in parliament to be elected.

Beleaguered Palestinian guerrillas and many Lebanese politicians say the Saudis are likely to demand in exchange an honorable solution to the dilemma facing the PLO.

Were the Saudis to succeed in persuading Gemayel to moderate his public demands--a refusal to countenance any armed Palestinian presence or even a meaningful political role in Lebanon--then political forces could be put in motion that would result in the collapse of the already debilitated presidency of Elias Sarkis, according to analysts.

The United States officially has equated its own policy for solving the Palestinian and Lebanese problems with that of the rump Christian-dominated Sarkis regime despite growing Lebanese Moslem reservations.

Washington and Riyadh, in the view of analysts here, apparently are seeking to substitute a moderate Arab influence guaranteed by the United States for the embarrassing prospect--in Arab eyes--of an Israeli protectorate over Lebanon.

Nonetheless, the effort appears fraught with great danger. That the United States agreed to risk such deep involvement in Lebanon's treacherous politics was considered a measure of American desperation to save West Beirut.

"Begin must be scratching his head wondering what is going on," one Palestinian official said.

Saeb Salam, the veteran Sunni Moslem former prime minister who has worked to find an honorable solution for the Palestinians, made clear to reporters this afternoon that he was not pleased.

Although a close Saudi ally, Salam expressed the traditional Moslem leadership's resentment of the effort. "It is a false way of doing things," Salam said.

Nabbih Berri, the leader of Lebanon's Amal militia, representing the Shia Moslem community, expressed similar surprise and reservations in an interview.

Despite the suddenness of Gemayel's mission, both the United States and the Saudi monarchy have been cultivating ths young militia commander for some time.

Saudi Crown Prince Abdullah long has been a close associate of Gemayel's father, Pierre, founder of the right-wing Christian Phalange Party, which provided Bashir his political and military start.

Shared conservative politics have kept this odd alliance together except during the civil war, when the Saudis--upset by perceived Christian excesses--cut off funding and political support.

The United States for years kept Bashir Gemayel at arm's length. But last year, when he was at his lowest ebb--after provoking the Syrians at the Christian mountain town of Zahle in the vain hope of bringing the Israelis in on his side--the United States for the first time officially invited him to Washington.

Gemayel's theme of "defending the free world" struck a chord with the Reagan administration and congressional conservatives such as Sen. Jesse Helms (R-N.C.).