Syrian Foreign Minister Abdul Halim Khaddam returned to Lebanon today, but hopes of easing the five-week-old hostilities between Christian militia and Syrian troops that has led to an Israeli-Syrian missile crisis here faded as Khaddam showed no intention of holding an announced meeting with key Christian militia leader Pierre Gemayel.

Militia sources said Gemayel's son, Bechir, who is the militia commander, had not seen a key Syrian military negotiator as planned over the weekend to smooth the way for continuation of the formal talks that began here last week.

Further complicating the tortuous Lebanese problem was the failure of the Phalange Party, which controls the largest Christian militia, to meet Syrian demands to issue a statement criticizing Christian links with Israel.

Nonetheless, Western diplomats expressed hopes that progress in the talks could help lead to a face-saving formula allowing Syria to remove its Soviet-built SA6 ground-to-air missiles from the Bekaa Valley, a strategic portion of eastern Lebanon.

Mutual militia and Syrian concessions, these diplomats suggested, could create the impression that a package deal had solved many of the immediate outstanding security problems.

Thus, for example, the Syrians could claim success if the militia removed its troops from the predominantly Christian city of Zahle, which has been under Syrian siege since April 1.

In turn, if the Syrian Army abandoned its positions along the strategic Lebanon Mountain ridge line overlooking the Bekaa Valley and the Christian heartland to the west, both the militia and Israel, which has said it would defend the Christians, could claim victory.

It was the Syrian mountain offensive that set off the larger crisis when, after a State Department statement criticizing this "major change in the status quo," Israeli warplanes last week shot down two Syrian helicopters used in the mountain action.

The loss of those helicopters was invoked by Syria to justify the installation of the antiaircraft missiles in what it called a purely defensive measure.

Such a break in tensions -- accompanied by moves such as the reopening of Beirut Airport after 13 days of closing -- could be cited by Syria as evidence of its success, the diplomats argued, and the missiles could be removed without suggesting humiliation.

Some Lebanese observers, however, were pessimistic about any breakthroughs. Their arguments were based on the reluctance of the United States to press Israel to approve the militia's withdrawal.

Although the fighting has slacked off during the last week, its repercussions are still being felt. In April, which saw the worst fighting since the end of the 1975-76 civil war, officials said 452 persons were killed and 1,170 were wounded.