'WHAT on earth is Hafez al-Assad up to now?" This was the suspicious tone of much of the commentary after Syria's powerful president signaled acceptance of Washington's formula for Mideast peace talks.Does Mr. Assad truly wish to contribute constructively to present peace diplomacy? There is one foolproof way to find out: Put his promise of cooperation to the test. The widespread skepticism over Assad's intentions came at the end of a decade in which Americans often judged him "Mideast villain of the month." It was Assad, the Reagan people said, who scuttled the peace agreement between Israel and Lebanon in 1983. It was Assad whom many Americans blamed for the continued holding of hostages in Lebanon. It was Assad they accused (wrongly, it now seems) of having masterminded the bombing of Pan Am Flight 103. Assad's name is Arabic for "Lion," and it is evident that he's no pussycat. But then, there are few leaders anywhere in that part of the world who do not also have massive human rights abuses on their records. Meanwhile, there are other items on Assad's resume that should force us to take seriously the contribution that he could make, if he wished, to Mideast peace diplomacy: * Since the end of 1973, he has accepted that Security Council Resolution 242 be the basis for Arab-Israeli diplomacy. * In July 1974 he concluded a disengagement agreement with Israel that made the Golan Heights the most impervious sector in Israel's entire defense perimeter. * From 1976 to 1982, and again from 1985 to the present, he coordinated the movements of his troops in Lebanon with Israel's activities there. (In 1981 and 1982, it was Israel, not Syria, that broke the "Red Lines" agreement in Lebanon.) But still the question lingers. Why would Assad want to buck Arab nationalist rhetoric and contribute to diplomacy? Having just completed a study of Syria's policy toward Israel, I will hazard guesses. His major motivation is to see, in concrete terms, just what he can get out of such a negotiation. Assad's main strategy toward Israel has been to achieve an elusive "strategic parity" with the Jewish state. His foreign minister, Farouk Sharaa, told me in 1987 that such parity equaled "the sum of our own capabilities, plus the commitments we would have from our superpower backers." Mr. Sharaa and his boss understood some time ago, however, that any "commitments" Syria once had from the Soviets have totally dissolved. Meanwhile, the local power-balance between Israel and Syria continues to tilt in Isra el's favor. So if strategic parity is impossible to achieve, what option does a Syrian president have for dealing with Israel's continued occupation of Syrian territory in the Golan? Actively entering the diplomacy of land-for-peace must seem like the next-best option. After all, the newly energized United Nations Security Council made a point when crafting last fall's resolutions condemning Iraq to use the same language used in Resolution 242, stressing "the inadmissibility of the acquisition of territory by force. " Is there a land-for-peace deal to be done on Golan? That strip of territory is, after all, vital for Israel's security - towering over the north of Israel's heartland. Israelis of all political colors have stressed it would be impossible to have Syrian gunners once more sitting atop the Heights. But that does not mean that Israel's gunners (or settlers) have any right to stay there. If Golan were effectively demilitarized under international supervision, and Israel concluded a peace agreement with Syria, then both countries could divert substantial portions of their current military expenditure back to economic development. Both would end up more prosperous and secure. Is such a plan to defuse the tension between Israel and its most heavily-armed Arab neighbor only a pipe dream? It should not be judged as such. The present Syrian and Arab climate of conciliation toward Israel will not last forever. If the peace process stalls, and Israel continues putting settlers in the occupied areas, there are still forces of instability in the Middle East that could bring chaos back to the region. Saddam Hussein is still in Baghdad, playing his horrendous nuclear shell-games. He must be waiting for the failure of the current diplomacy in order to get back at those Arab "brothers" who fought against him - with Syria near the top of the list. Rather than wait for that to happen, let's hope President Bush puts Assad's intriguing promise of cooperation actively to the test.