The Soviet Union has urged Syria not to escalate the current confrontation with Israel into a full-scale war but has not tried to persuade Damascus to withdraw its Soviet-made surface-to-air missiles from Lebanon's Bekaa Valley as Israel has demanded, according to Western and Asian diplomats here.

Indeed, it is widely believed in the diplomatic community that the Soviets would replace immediately any missiles out by the Israels.

No matter how much Moscow wants to prevent another Middle East war, which it and the United States could be dragged intgo diplomats here say it cannot afford to anger Syria -- its major toehold for influence in the region -- by pressing it to withdraw the missiles as the United States has.

While Syria receives the vast bulk of its arms from the Soviet Union and the two nations signed a 20-year friendship treaty in October, Moscow is not seen as having much influence over the regional policies of Syrian President Hafez Assad.

"Syria is not a Soviet puppet," declared one West European diplomat.

The Syrians reportedly did not consult with Moscow when they moved the missiles into Lebanon more than two weeks ago.

The Soviets were said to be so angered last December when Assad moved two Army divisions to the Jordanian border in a conflict with King Hussein that they considered canceling a high-level visit.

Although Moscow appears unable to exert much influence over Syrian actions in the region, the Soviets are seen here as having reaped major gains from the current Syrian-Israeli confrontation.

By this account, the Soviets could expect to participate in any negotiations on comprehensive Middle East settlement, a position denied them by the Camp David agreements, and are likely to be needed as a guarantor along with the United States of any deal that President Reagan's special envoy Philip C. Habib can fashion to end the current dispute.

Perhaps more important for the Reagan administration's global strategy, the return of Arab-Israeli confrontation to center stage has endangered Secretary of State Alexander M. Haig Jr.'s concept of a "strategic consensus" that would enlist the Arab nations of the Persian Gulf and Pakistan as allies to prevent Soviet expansion into that oil-rich region.

The current crisis is seen here as bolstering the view of many Arab nations that settling the longstanding Arab-Israeli dispute is more important for the stability of the region than confronting the Soviets. This view formed the cornerstone of Arab responses to Haig's concept during his Middle East tour last month.

The confrontation furthermore threatens to complicate U.S. relations with Saudi Arabia, Egypt and the oil-rich states of the gulf and to achieve a major Soviet objective of scuttling American plans to build a viable defense force in the region.

"It has been a major tactical error by the Israelis," said one diplomat of Israel's demand that Syria withdrew the missiles put into the Bekaa Valley after Israel downed two of its helicopters operating there as part of the Arab deterrent force in Lebanon.

Syria, meanwhile, is making much of its Soviet connection. An editorial this week in Al Baath, the newspaper of the ruling Baath Socialist Party warned that an Israeli attack on the missiles would challenge "the strategic will of Syrian-Soviet friendship and cooperation."

It is not believed the Soviets would go to war if Israel mounts a quick strike against the missiles in the Bekaa Valley and on the Syrian-Lebanese border and left it at that. But in the view of these Asian and Western diplomats here, any military escalation increases the threat of more Soviet involvement through a major resupply effort.

As of now, Syria and the Soviet Union -- despite the friendship treaty -- have an essentially simple relationship of one country supplying arms to the other. But a major resupply effort is in the midst of a war with Israel is seen as a possible wedge to incresae Soviet influence here.

There are already 3,500 Soviet military advisers here, along with a slightly smaller number of East Germans who act mainly as instructors in the maintenance and repair of the more sophisticated weapons sytems. None of the advisers is believed to be with the Syrian troops in Lebanon.

Last year, the Soviets began supplying Syria with their most modern tank, the T72. There are now believed to be 500 in Syria and more are reported on the way.

While the Soviets long have been Syria's major arms supplier and there is a widespread feeling of gratitude here for Moscow's help in supporting and arming Syria during the 1973 war with Israel, relations between the two countries have had rocky periods.

Four years ago, Moscow was miffed at Syria for taking on the Palestine Liberation Organization in Lebanon. At that time, Assad appeared to seek a middle course between the United States and Soviet Union, traveling to Geneva to see then president Carter shortly after a visit to Moscow.

A year-long estrangement between Damascus and Moscow ended only in the late 1979 after an Assad trip to the Soviet Union, which produced the promise of more Soviet arms. Diplomats say Syria initiated discussions for the friendship treaty as a means of countering its growing isolation in the Arab world.

Along with Libya and the PLO, Syria fought moves last year by the Islamic Conference to condemn the Soviet Union for its invasion of Afghanistan, arguing that such a policy by the Moslem states would play into U.S. hands and distract attention from the Arab-Israeli dispute.