Thaw in US-Syria relations will be tested by events. US envoy to return, but areas of potential friction persist

Although the Reagan administration is sending its ambassador back to Syria, United States offiials caution that this positive step should not obscure major differences that remain between the two countries. Ambassador William Eagleton was recalled from Damascus last fall after Syria was implicated in the attempted bombing of an Israeli arliner in London. The decision to send him back, perhaps next month, stems in part from Syria's possible role in the return to freedom last week of American jounalist Charles Glass, who was kidnapped by terrorists in Lebanon in June. The White House announced Saturday that President Reagan sent a cable to Syrian President Hafez Assad thanking him for Syrian efforts to free Mr. Glass.

Syria is strategically important because of its common border with Israel and its major influence in Lebaon. Thus, Washington should have an ongoing high-level dialogue with Damascus, US officials say.

But that dialogue has been impaired by Syrian behavior offensive to the United States. Indeed, many US officials continue to doubt that Washington can have a productive relationship with President Assad.

One US specialist explains that the Reagan administration, like its predecessors, has regularly debated whether Syria is susceptible to the inducements and pressures that led Egypt to deal with Israel and to establish close ties to the US. State Department officials contrast Syria with Jordan, another Arab state, which US officials view as a potential partner.

Officials identify four areas by which to measure the potential for US-Syian relations:

Arab-Israeli peace prospects. In times of Syrian-Israeli military tensions, a channel of communication with Damascus is vital. But officials sy Syria does not share US views on how to approach a solution to the conflict. While some US officials say Syria wants only to regain the Israeli-occupied Golan Heights, others argue that President Assad is not willing to accept Israel's existence.

Lebanon. Officials see a possible convergence of US and Syrian interests. Both want to avoid the reemergence of an independent Palestinian movement in southern Lebanon and in preventing the entrenchment of a radical Shiite Muslim presence in Lebanon. Syria also seems to agree on the need to restore order and a coherent political framework to Lebanon. The problem, sources say, is translating these interests into a workable agreement, especially when Israel is figured in.

Iran-Iraq war. Damascus remains Iran's sole Arab ally. This relationship began as a tactical move by Assad to outflank Iraq, a traditional enemy, and to get cheap oil. There are evident tensions between Tehran and Damascus, particularly over support for the radical Shiite Hizbullah movement in Lebanon. Despite the tensions, however, some US officials wonder if Damascus will relinquish ties with Iran. One analyst asks, ``Would US and Syrian interests coincide if Iran achieved a military breakthrough against Iraq and threatened the strategic balance in the region?''

Terrorism. After recalling Ambassador Eagleton in October, Washington told Syria to clamp down on terrorists operating out of Damascus if it wanted improved relations with the US. Since then, Syria has closed the Damascus offices of terrorist Abu Nidal and, with pressure from Turkey, restricted Armenian and Kurdish terrorists. Washington decided these steps were enough to send its envoy back to Damascus. But US officials still say Syria is far from reformed and could well use terrorism again as a policy tool.

On top of this, Damascus has close ties to Moscow.

Yet US officials agree that President Assad is extremely shrewd and pragmatic. He wanted to end his diplomatic isolation and have the status of full relations with the US, so he took a few steps, they say.