Syrian Foreign Minister Abdul Halim Khaddam flew to Moscow today seeking what is described here as a "qualitative change" in Syria's already close military and political ties with the Soviet Union to counter the U.S.-Israeli alliance.

Informed Syrian and Western diplomatic sources said Khaddam would sound out Soviet willingness to sign a strategic cooperation agreement with Syria--to match the one signed by Washington and Tel Aviv late last year--that would include a Soviet commitment to defend Syrian troops stationed in eastern Lebanon.

If Kremlin leaders agree to such an accord, Syrian President Hafez Assad is expected to visit the Soviet Union to sign it, a move that seems certain to worsen already tense relations between Syria and Israel.

Western analysts here are extremely doubtful Moscow will agree to Syria's request for a firm commitment to defend its positions in the Bekaa Valley of Lebanon. They note that Moscow is preoccupied with Poland right now and that in the past Soviet leaders have been very reluctant to get involved in the Lebanese quagmire.

Syria, however, hopes that the Soviets' anger at the U.S. sanctions against Poland and the Soviet Union will stir them to take a firmer stand in defense of Syria.

Syria's quest appears at least partly related to the failure of the U.N. Security Council to take strong action against Israel in retaliation for its annexation last month of Syria's Golan Heights.

The state-controlled news media here have put full blame for this on the United States, which they accuse of "double-dealing" in demanding Western sanctions against Poland and the Soviets while opposing them against Israel even after a unanimous Security Council resolution condemning the annexation.

Khaddam had warned in a recent newspaper interview that Syria would seek a strategic cooperation pact with the Soviet Union if the Security Council took no significant measures to punish the Jewish state.

Last night, Assad said in a speech here that Syria's recovery of the Golan Heights depended on a balance of power in the Middle East and warned that "international law permits Syria to recover its sovereignty over the Heights whenever and however deemed necessary."

This desire to establish a balance through a further arms buildup and a closer military alliance with Moscow to all appearances has become a principal preoccupation of Syrian diplomacy right now.

Syria and the Soviet Union signed a treaty of friendship and cooperation in 1980 that calls for joint consultation and action in case of a threat to peace in the region. But more important in Syrian eyes is a declaration by Soviet President Leonid Brezhnev in 1974, during a visit of the Syrian president, committing the Kremlin to defend Syria in case of outside aggression.

Informed sources here said that one of the main points of discussion between Khaddam and Soviet leaders will be a closer definition of just what constitutes "aggression" against Syria, principally by Israel. The sources said Syria wants a Soviet commitment for assistance not only in case Israel attacks Syrian territory but also if it strikes against Syrian forces stationed in Lebanon as Arab peace-keeping forces.

Israel's annexation of the Golan Heights and threatening statements by Israeli officials against Syria and the Palestine Liberation Organization have raised considerable fear here that Israel is planning a major strike against Palestinian guerrilla bases in southern Lebanon.

There is concern in Western diplomatic circles here that the Soviet price for signing an even vaguely worded strategic cooperation agreement with Syria might be greater Soviet access to Syrian military facilities, possibly the permanent stationing of reconnaissance planes or even something close to formal bases, which Syria so far has refused.

Syria also reportedly is seeking more Soviet arms and an advanced antiaircraft missile defense system as part of its defense against Israel.

The Soviet Union already has begun to modernize Syria's armed forces, principally by providing newer and heavier T62 and T72 tanks to replace outdated T54s and T55s. Syria has about 3,700 tanks, 200 more than Israel, according to the International Institute for Strategic Studies.