Using Soviet military aid and a risky strategy of brinksmanship that forces other Arab states to pay court, Syria has bounced back from its humiliating defeat at Israeli hands a year ago to the center of Middle East politics.

In the past few days, Syria has played host to leaders as varied as Saudi Crown Prince Abdullah, Algerian President Chadli Bendjedid and Arab League Secretary General Chedli Klibi--and at the same time has refused to receive special U.S. envoy Philip C. Habib.

The presence here of the Arab dignitaries underscored Syria's key role in two critical regional problems:

* Its rejection of the Israeli-Lebanese agreement on Israeli troop withdrawal from Lebanon.

* The mutiny within the ranks of the Palestine Liberation Organization.

Syria's reemergence as a major regional player is based less on a self-assurance that some diplomats worry masks unjustified confidence than on the very real problems besetting its neighbors and the United States.

"We think time is on our side and we will not give up," insisted Information Minister Ahmad Iskander in explaining Syria's refusal, so far at least, to accept the American-backed Israeli-Lebanese agreement and, indeed, its determination to foil it.

"We think the ball is in the American court," he added.

How close Syrian President Hafez Assad is to the brink remains to be seen. The tension late last month--stemming from a Syrian air-to-air missile fired at an Israeli plane, Syrian Army maneuvers and the sudden appearance of at least one Israeli brigade in Lebanon's southern Bekaa Valley--suggested that the risk of renewed major fighting remained very real.

But in the meantime Syria successfully has stymied the weak Lebanese government's efforts to increase its stature by negotiating the departure of all foreign forces.

The Syrian government appears to be convinced that the pressures of attacks by Lebanese and Palestinian guerrillas on Israeli troops in Lebanon, the failure of King Hussein of Jordan to come to an agreement with the PLO on peace negotiations and the continuing troubles arch-rival Iraq faces in its war with Iran have diluted the efforts of Syria's neighbors to isolate Assad's rule.

The deep Syrian suspicion that the United States sought to orchestrate an effort by Syria's neighbors to isolate it has had strong impact on the Syrian rejection of the Israeli-Lebanese troop withdrawal agreement, which Damascus denounced as a "pact of submission" and as "Camp Shultz"--that is, Secretary of State George P. Shultz's variation of the hated Camp David accord.

Iskander, the information minister, said in an interview: "The Reagan administration thinks that it is able to impose what it wants on the Middle East. That is an illusion."

Iskander reiterated Syrian demands for junking the Israeli-Lebanese agreement as the price for improving relations with Washington.

But diplomats wonder openly if Syria has enough muscle to justify a policy of calculated defiance despite its Soviet aid.

Replenishing Syria's defeated arsenal has helped the Syrians forget the anger displayed toward Moscow throughout last summer.

Two Soviet SA5 ground-to-air missile sites have been installed in Syria with 1,500 Soviet troops manning and guarding them to frustrate the kind of airborne electronic warfare advantage that helped Israel knock out Syria's air defense system in Lebanon and destroy 98 jets and helicopters last year. There are an estimated 3,000 other Soviet military personnel serving on fixed term or temporary duty in Syria.

Iskander insisted the Soviets "have made it clear for the past two months" that if there is a clash with Israel "Syria will not be alone." He reiterated the assurance that Soviet arms "are supporting Syrians wherever the Syrians are," suggesting that Moscow would protect the estimated 45,000-man Syrian force in Lebanon.

When reminded Syria had looked foolish in proffering similar assurances last year, Iskander replied: "We are in 1983."

Syria seemed to be trying to communicate that message when a Syrian plane fired an air-to-air missile at an Israeli reconnaissance aircraft 10 days ago. This was meant, according to military specialists, as a signal that for the first time Syria had an operational surveillance network and early warning system.

Unlike last year, when Syrian air defenses were rudimentary, the incident indicated that the Syrians were able to spot and localize intruders and scramble pilots waiting in aircraft, all in time to engage in combat only miles inside Lebanon.

Military specialists, however, remain dubious about the Syrians' ability against the Israeli Air Force. They note that the SA6 surface-to-air missiles so easily knocked out in the Bekaa last year have now been moved back to Syria proper with only low-level SA8s and SA9s left inside Lebanon. The specialists suggest that the normally cautious Soviets could very well fire the SA5s only after a first strike by the Israelis, who are still credited with the ability to knock out Syrian-manned air defenses.

For the moment, Syria seems content not to take any drastic actions and to move slowly.

"For Syria," a western diplomat noted, "Lebanon has a very low sense of urgency," but for the United States not only its credibility but also 1,200 marines are at risk in the chaotic situation there.

What Syria really wants short of canceling Lebanon's deal with Israel is the best kept secret in town. Many diplomats are convinced Assad may not yet have made up his mind.

But even optimists expected no big change in Syrian policy and warned that the best hope to bringing Syria into the peace process lay in broadening any negotiations well beyond the narrow scope of troop withdrawal from Lebanon.

The options vary from the American hope that Syria would cut a similar, perhaps more advantageous deal, with Lebanon to diplomatic action on the occupied Syrian Golan Heights which Israel annexed in 1981. Other options included increased Saudi largesse or an international peace conference including the Soviets and the PLO, or a combination of some of these.

In the meantime, there are already worrying signs Syria intends to increase pressure on Lebanon to combat the agreement with Israel. Syria is strengthening an anomalous opposition to the Lebanese government loosely linking the Druze leader Walid Jumblatt in the Chouf Mountains, Lebanese communists, former Maronite Catholic president Suleiman Franjieh and Tripoli Sunni Moslem leader Rashid Karami in the north. To show its resolve, Syria also sent back into Lebanon last month the Hittin Brigade of the Palestine Liberation Army it controls.