For more than two months now, the Russians have been issuing dire warnings about a new Middle East crisis. Initially, daily forecasts about impending Israeli attacks on Syria were ignored, overshadowed by the drama over deteriorating East-West relations focused on the planned deployment of new American nuclear missiles in Europe.

More recently, however, the Soviet propaganda and the unpredictable pattern of Middle East diplomacy have led to speculation that the Russians may be serious and that they may welcome a crisis while not being prepared to initiate one.

Several reasons for this view were advanced in conversations with foreign and Soviet sources.

One is that the Kremlin would welcome a chance to rehabilitate the reputation of its weapons destroyed last year in the Lebanon conflict. The Soviets were especially embarrassed that the Israelis easily destroyed Soviet-made SA2 and SA6 surface-to-air missiles deployed by the Syrians in the Bekaa Valley.

Another reason is that a new Arab-Israeli war may serve as a shock capable of putting at least a temporary halt to the war between Iran and Iraq, something that the Russians would like to see.

Yet another and perhaps the most significant reason is that the Russians feel politically and diplomatically cornered and apparently unable to break the impasse in their relations with the United States. This has produced a sharp decline in East-West relations that conceivably could be arrested and reversed by a major international crisis. "To ease the pressure you pierce the boil at the edges," said one observer familiar with Kremlin tactics.

It is the prevailing view here that Syria and its Soviet ally are not going to initiate a conflict and that they would wait for an aggressive action by Israel. But Syria's military preparations and Moscow's daily rhetoric about an impending Israeli attack suggest elements of a self-fulfilling prophecy.

Since the Israeli invasion of Lebanon, Moscow has replaced the Syrian arms lost in last summer's fighting. But the Russians also have delivered some additional new hardware, including their most advanced SA5 surface-to-air missiles, and have dispatched several thousand military specialists to Syria.

According to the sources, the quality of these missiles and their range--they can hit aircraft over Israeli territory--could for the first time put Israel's Air Force to a severe test. Israeli air superiority in previous Middle East wars has been a key ingredient of its power.

There also are reports that the Russians are building an integrated air defense system for Syria and that they are placing equipment there that previously was deployed only in the Soviet Union.

Some diplomatic sources here say that the Russians have put in their SA5 missiles and personnel in Syria to deter a new Israeli attack. Others, however, say that the Soviets would like the opportunity to give Israel a bloody nose by bringing down a large number of Israeli aircraft if Israel attacks. According to that view, the reputation of Soviet arms bears directly on Moscow's influence in the Third World, and this reputation suffered last year.

The presence of SA5s manned by Soviet personnel makes clear that any attack on Syria includes the possibility of involving the Soviet Union.

In the regional context, the Russians apparently are seeing opportunities for making political gains. The war between Iran and Iraq is seen here as having inflicted damage to Soviet interests, including the weakening of the so-called "rejectionist" front of radical Arab states.

An Israeli attack on Syria, according to the sources, conceivably would provide a face-saving excuse to Iraq and particularly to Iran's leader Ayatollah Ruhollah Khomeini to halt the fighting in order to help a Moslem nation at war against Israel.

Short of a dramatic development, according to this view, it virtually is impossible for Moscow to do anything to influence Iran and Iraq. Moscow's relations with Iran have deteriorated with the arrest of leaders of Tudeh, the Iranian communist party.

Moreover, the war has had an impact on Afghanistan, the one issue that severely has narrowed the scope of Soviet diplomacy in the Third World and particularly with Moslem nations. As long as Iran is at war, it is argued, it could not be expected to join any attempts to resolve what the Russians call the problems "around Afghanistan."

Moscow has been reluctant publicly to take sides on the Iranian-Iraqi war. Recently the Soviets have stepped up aid to Iraq, and a high-level Iraqi delegation was reliably reported to have visited here last week for talks with Kremlin leaders. It is believed in diplomatic circles that one of the topics discussed was the way to end the war.

Well-informed Arab sources here say that relations between Syria and Iraq, both allied with Moscow yet at odds with each other, could be repaired only if a major crisis erupted.

While dealing directly with the Iraqis, the Russians are said to be dealing with Iran through Syria and Libya. Syrian President Hafez Assad received the Iranian foreign minister in Damascus last month, and it was believed that Assad had raised the question of air and ground access for Soviet supplies in case of an Israeli attack on Syria.

The Syrians also upgraded their diplomatic representation here six weeks ago by sending a former prime minister, Mohammed Ali Halaby, as ambassador. The post had been vacant for almost two years.

The sources stress that the calculus of Middle East politics now has to include the drop in oil revenue for many conservative Arab states and possible social and political consequences that this may entail. The Russians believe that President Reagan's Middle East peace initiative has come to a dead end and that radical Arab forces are likely to come to the fore in coming months.

One imponderable in all this speculation is the situation in Lebanon. While it seems clear that Syria has no intention of attacking Israel, the presence of Syrian and Israeli troops in Lebanon provides for an explosive atmosphere in which a conflict could be generated. There is speculation in well-informed circles that an armed confrontation in Lebanon could bring Soviet rockets into action should Israel use airpower against the Syrian contingent in the Bekaa Valley.

The main concern of Soviet sources is the impact of another Middle East war on overall East-West relations. What they seem to feel is that only the risk of a major confrontation may produce a meaningful dialogue between the superpowers.

Moscow, obviously, does not want a direct confrontation with the United States. But the unrelenting political and propaganda pressure seen here as having been orchestrated in Washington has produced a sense of frustrated isolation while the Americans steadily push toward their perceived goal of gaining military superiority.

In this atmosphere, diplomatic observers say, the Russians may be tempted to take up the challenge of a confrontation by proxies. The Middle East, because of its proximity to Soviet borders and possible political benefits there, is perhaps the only area at the moment where Moscow can inflict damage to U.S. interests and America's allies.