Friction Growing Between US, Syria. US concern mounts over terrorism, Lebanon, and Assad's obstruction of peace efforts. ANALYSIS

SYRIA and the United States may be heading toward sharp disagreement over terrorism, Lebanon, and the Middle East peace process. As investigators move toward their conclusions on who bombed Pan Am Flight 103 over Scotland, the prime suspects continue to be operatives of a radical Palestinian group based in Damascus, the Popular Front for the Liberation of Palestine - General Command (PFLP-GC). The discovery of four more sophisticated bombs tied to the PFLP-GC in West Germany has reinforced suspicions.

The US has privately told Syria that although there is no proof of direct Syrian involvement, it is a case of guilt by association because Syria shelters the group, say sources informed of the exchanges. The Syrians have responded that they will not cashier the group without proof.

If investigators find proof, the Bush administration will be under great pressure to use full US leverage to get Syria to act.

As fighting in Lebanon continues, Washington is increasingly critical of Syria's heavy bombardments of Christian East Beirut and its obstinacy in arranging a cease-fire there. The US does not want to get too involved in Lebanon, but if fighting continues it may have to do more, Arab and European diplomats say.

As the Bush administration proceeds in its step-by-step approach to peace between Israel and its neighbors, Syria remains the most likely potential spoiler. A number of key US officials suspect Syria will do its utmost to derail the process. Some hope the Soviets will use their influence to moderate Syrian behavior and bring them toward peace.

``We're clearly on what could be a collision course'' over these issues, says a senior US diplomat. But it is not yet clear if the collisions will take place or if solutions can be found, he says.

Patrick Seale, author of a new biography of Syrian President Hafez Assad, entitled ``Assad: The Struggle for the Middle East,'' says Lebanon and the Middle East peace process are life-and-death issues for Mr. Assad.

``Promoting a peace settlement that excludes Assad will drive him to the wall,'' Seale says. If that happens, Assad ``will fight back and fight dirty.'' On Lebanon, he adds, Assad fears that ``if he loses control, he could well be finished'' at home as well as cede influence in that country to Israel.

Similarly, Seale explains that Assad is not going to move against a valuable ``proxy'' like the PFLP-GC just because of charges in the press. Groups like the PFLP-GC are ``important instruments in Assad's broader struggle'' to contain Israel and to keep others like the Palestine Liberation Organization (PLO) from signing a partial peace, he says.

Syria's leaders may not be totally aware of the triple whammy building momentum in the US, Seale says. The Syrians are not that well plugged into Washington. President Assad has come to feel that whatever he does it will be tough to be understood in Washington, because Israel will work to turn everything against Syria, the British author says.

Syria remains Israel's most implacable foe at present and President Assad remains bent on winning peace through strength. Assad has for years sought to establish a balance of forces in the Eastern Mediterranean that will contain Israel, says Seale, who spent hours interviewing Assad and his close collaborators.

Assad, Seale says, sees himself as striving to build a peace that can be maintained by Arab strength. Seen critically, Seale adds, this looks like an effort to build a greater Syria in Lebanon, to establish Syrian hegemony over the Palestinians and to threaten Israel. ``But the Syrians see themselves as the threatened ones.''

Assad is willing to negotiate peace with Israel in an international peace conference without preconditions, Seale says. But the Syrian leader maintains that no solution is better than one which institutionalizes Israel's dominance. Thus, Assad disrupted the US-brokered Israel-Lebanon treaty in 1983 and efforts to work out an Israeli-Jordanian accommodation in the mid-1980s.

Assad also opposes efforts to bring the PLO and Israel together. He sees PLO chief Yasser Arafat as ``making concession after concession,'' Seale says, and thinks Palestinians ``will be eaten alive by the Israelis if they ever get to the negotiating table.''

While the gaps will be very hard to bridge, Seale says there can be no lasting peace in the region without Syria. US officials agree Syria cannot be excluded, but they do not have pat answers on how to engage Damascus in the US approach to peace.

Current US strategy is to explore the possibilities for Palestinian-Israeli dialogue, while building barriers and incentives that diminish the ability and interest of Syria and others to disrupt initial steps toward peace.