With his forces besieged by Syrian troops in the town of Zahle, Christian militia commander Beshir Gemayel called today for a complete cease-five in Lebanon.

In 13 days of fighting the all-Syrian Arab Deterrent Force had succeeded in tightening its grip around the city of 160,000, but the Syrians so far have failed to obtain the surrender of the Christian militias.

Military sources in the Christian Phalangist War council said "all hilltop positions in the immediate environs of Zahle were now in Syrian hands, thus making access to it by the militias virtually impossible without a major battle." The Phalangists are the dominant force among Lebanon's Christians.

The Arab Deterrent Force was set up late in 1976 to bring an end to almost two years of civil war in Lebanon and has remained in the country ever since. At stake in the fighting around Zahle and in Beirut is control over the newly revived Lebanese Army. The Syrians want control of Lebanese Army units in the Zahle area, which sits astride the strategic Bekaa Valley and its access to southern Lebanon.

The Syrians now are in a position to maintain a stranglehold on Zahle and the Phalangist militia holed up in the city. At the same time, they so far have not been able to chase the Phalangists from the city. Any further fighting is likely to be bloody affair, something Gemayel apparently realizes given his statement today calling for a cease-fire.More than 300 persons have been killed in the fighting in Zahle and Beirut.

While seeking talks to end the fighting, Gemayel declared a victory, saying his militas had succeeded in stirring international concern over Lebanon.

In an interview with the Phalangist party radio Voice of Lebanon aired early today, Gemayel said "we have won the battle politically, and consequently this is the greatest military victory for our causes."

As light shelling continued around Zahle, the Parliament building in Beirut came under mortar and machinegun for three hours, until soldiers from both sides of the Moslem-Christian dividing line whisked the Cabinet ministers and deputies meeting there to safety. Syrian forces and the Christian militias accused each other of starting the shooting.

Commenting in his radio interview on Western condemnation of Syrian shelling aimed at Zahle and Lebanese Army positions along Beirut's dividing line, Gemayel said, "Talk about initiatives is not enough."

"We ask for extra help and that is not for batteries, blankets, Mercurochrome or milk for our babies," he added. "We need a political commitment to preserve Lebanon as free, independent and master of its own decisions and choices."

Gemayel also insisted that the outside world should come forth "with an operational commitment" without giving any details on what form it should take. o

"When someone wants to help effectively, he will find ways to come to our rescue," he said.

"Any door from which we can exit from this crisis with agreement, a dialogue or understanding is adequate," he added.

He said his group would walk into negotiations with the Syrians with its "head held up high" because of the many sacrifices it has made so far.

Eager French diplomatic moves to call for a Security Council meeting and a U.N. policing force to replace the Syrians in Lebanon have not come to fruition. They were stymied by a split within the Lebanese governmemt. Moslem officials see an international force as necessarily sympathetic to the Christian community at Moslem expense. They also say a Soviet veto can be expected in the Security Council.

Syria, the Arab League, the Palestine Liberation Organization, Lebanon's leftist National Movement, Lebanese Sunni Moslem and Shiite leaders as well as moderate, oil-rich Kuwait have spoken against "internationalizing" the Lebanese crisis.

Syrian Foreign Minister Abdel Halim Khaddam yesterday accused France of joining the United States and Israel in "provoking" the Syrians. fToday's afternoon Radio Damascus commentary lashed out at France, criticizing it for "confounding its past historical ties with Lebanon with its present realistic interests."

Syria's Information Minister Ahmed Iskander Ahmed told the Paris daily Le Monde that Syrian forces would not leave Lebanon unless they are asked to do so by the Lebanese government. A highly placed U.N. source, familiar with the Lebanese government's line of thinking has said it was in no position to ask for U.N. forces, because of domestic opposition.

There were conflicting reports about the fate of Jordon's charge d'affaires in Lebanon. Hisham Moheisen, who was kidnaped Feb. 6. Some news sources said he had been released but there was no official confirmation.