Following inconclusive talks in Damascus, Lebanese President Elias Sarkis flew to Saudi Arabia yesterday as the two-day-old cease-fire between Syrians and Lebanese Christians showed ominous signs of unraveling.

There was a mood of skepticism bordering on despair here following sarkis' apparently fruitless weekend talks with Syrian President Hafez Assad and it was underlined by the occasional mortar round of sniper's bullet.

Further hampering Sarkis' now desperate efforts to satisfy both Christians and Syrians was a successful general strike in predominantly Moslem West Beirut called to protest the president's security plan.

The plan - featuring replacement of Syrian troops in East Beirut by untested units of the Lebanese army which fell apart in the 1975-1976 civil war - has been implicitly rejected by Assad and his leftist and Moslem Lebanese allies.

Backed by armed gunmen and machine gun-mounted jeeps, these groups, which had largely disappeared from view since the civil war, drove in coonvoys down West Beirut's streets.

Sarkis is seeking a compromise between Moslems and leftists, who are determined to keep the predominantly Syrian Arab Deterrent Force in Lebanon, and Christians who are dead set on preventing renewal of its mandate which expires Oct. 26.

Beirut Radio said that after a fourth meeting between Assad and Sarkis ended at dawn yesterday, the Syrian leader said, "We have covered three-quarters of the way in our discussions and are optimistic."

But he was the only optimist, judging from a nearly unanimous sampling of newspaper an diplomatic analysis.

Sarkis also appeared to have failed to persuade Assad to back his plan for a new Cabinet - made up politicians from leading warring factions - to replace his largely discredited technocrats' government.

Assad was said to want an overall settlement including thoroughgoing reforms of everything from the political system dominated by the Maronite Catholics to the army command, which is also a Maronite stronghold.

The only substantive remark from the long discussions in Damascus - which are to be continued after Sarkis returns from his visit to the Arabian Peninsula - was Lebanese Foreign Minister Fuad Boutros' call for a foreign ministers' conference in Beirut.

It would group both the countries providing troops for the deterrent force - monstly Syria, Sudan, Saudi Arabia, North Yemen and the United Arab Emirates - and its bankers, insome cases the same countries.

A possible Sarkis goal would be to persuade other nations of the deterrent force to replace the Syrians inside East Beirut. The Christian leadership, however, wants all foreign troops out of all the country.

The Christians are given almost no chance of achieving that goal, since a total Syrian withdrawal would risk encouraging the militias to attack the Moslems and Palestinians and reignite the 1975-1976 civil war.

Meanwhile, mounting evidence indicated that the Christians had exaggerated both the destruction and loss of civilian life in the latest round of fighting.

Officials of the International Committee of the Red Cross suggested that no more than 400 civilians were killed - less than half the total claimed by the Christian spokesmen.

Similarly, they reported that medical supplies in the Chrisian areas were in better shape than had been expected.

However, Western intelligence sources estimated that the Christian militias lost as many as 100 to 150 men - almost double the casualties admitted publicly. Syrian loses were put by same sources as "at least" 200 to 250.