Damascus, Syria — The trucks laden with ammunition boxes growl up the road from Damascus into Lebanon, apparently resupplying antigovernment forces for a fresh round of battle with the US-backed President, Amin Gemayel.
That another round was irrevocably under way seemed, to gloomy foreign diplomats Tuesday, increasingly likely. American diplomats here declined comment. The rationale behind the more pessimistic view of other diplomats here was this:
Despite the capture of west Beirut last week by Mr. Gemayel's Syrian-backed Druze and Shiite Muslim foes, neither the weakened Gemayel nor his American patrons yet seem inclined to deal politically on the opposition's terms.
The United States naval force off Lebanon's shore was said Tuesday to have complied with a Gemayel request to resume, albeit on a relatively minor scale at time of writing, shelling of Syrian-controlled inland areas of Lebanon. Two Lebanese jets, most of Gemayel's tiny Air Force, went into action against opposition militiamen there for the first time in roughly five months. Unconfirmed reports from the opposition said one of the planes was downed.
Western news reports from Beirut said Lebanese Army troops had lost ground in the hills east of the capital in the escalated fighting. It was impossible to say with certainty who started the latest violence.
A visit by this and other reporters to east Lebanon after last week's larger-scale US naval bombardment suggested far less damage in civilian areas than Lebanese opposition spokesmen had charged. Yet in political terms, the shelling seemed to diplomats here an important sign that a negotiated detente in Lebanon was not around the corner.
Druze leader Walid Jumblatt, the Lebanese opposition's most vocal spokesman, insists Gemayel must resign, but is convinced the divided, weakened Lebanese Army is contemplating a US-supported counteroffensive.
Shiite leader Nabih Berri, arguably the opposition's most powerful spokesman, agrees Gemayel must go but seems more open to compromise on precisely how and when. Mr. Berri remains leery of aligning himself with Syria as closely as has Mr. Jumblatt, and feels internal Lebanese factors must dictate an eventual negotiated settlement.
Syria is believed ready to let Gemayel stay under certain circumstances. Also , the Syrians are, conditionally, open to the idea of having a United Nations force enter Beirut to replace the current US-European force there.
But what none in this three-voice opposition choir can countenance is the way in which Gemayel has responded to his military setbacks thus far: reaffirming links to the Americans and hanging on tighter to Lebanon's US-mediated May 1983 peace accord with Israel. Syria wants it scrapped.
Somehow, the Syrians seem to feel, US Mideast envoy Donald Rumsfeld should be conveying a fundamentally changed approach on the Lebanese crisis - not back in Washington merely weighing the next move with his highers-up.
Indeed, Damascus seems content and intent to wait until Gemayel and the US acknowledge politically what is seen here as an inescapably altered Lebanese balance of power. Meanwhile, daily convoys of Lebanese-registered trucks of ammunition, five tons per truck, resupply the Druze in the hills above Beirut.
The ammunition convoys from Syria are not new. But diplomats see their somewhat increased scale in recent days - reportedly peaking with an estimated 450-ton total one day last weekend - as evidence of a resupply of opposition forces after last week's fighting.
Talks here Tuesday, meanwhile, between Syrian Foreign Minister Abdel Halim Khaddam and various Lebanese opposition figures were interrupted by a phone call from Saudi Arabia's main mediator in the Lebanon crisis, Rafik Hariri. As Lebanese opposition sources tell things, Mr. Khaddam asked Mr. Hariri whether he had anything new to offer from Gemayel.
''Nothing earthshaking,'' was the reported gist of the reply, ''but we think it is a good time to talk to you on the general situation.'' Mr. Khaddam was reportedly noncommittal in his reply to that suggestion.
Saudi Crown Prince Abdullah is rumored to be planning to visit Damascus in a week or so. But the Saudis, if by Western views capable of exerting economic ''pressure'' on Syria, seem increasingly closer to Damascus's view than to Gemayel's on the crisis. And Saudi clout, even on paper, has been diluted of late by the Syrian government's diversification of foreign aid sources. Saudi aid of various sorts to Syria, still running nearly $1 billion annually, has gradually been overshadowed by at least equal support from Iran.
Syria maintains at least 40,000 troops in Lebanon - a force originally introduced with an Arab League mandate to end the 1975-76 civil war there. Damascus' military strength and Soviet-manufacture arms arsenal are a central factor in determining the political balance among Lebanon's own warring factions.
What does Syria want in Lebanon? The official answer is this: a scrapping of the May 1983 accord and withdrawal of all ''foreign forces.'' This means, in Syrian eyes, the Israelis who invaded in 1982 and the Western peacekeepers who arrived afterward. That force, because of US policy, has become ''a party to the conflict,'' Syria argues, propping up an ''unrepresentative'' Gemayel regime.
Various foreign diplomats - pointing to Damascus' past shifts in alliance during nine years of Lebanese civil strife - are convinced the Syrians ultimately would be willing to help ''save'' Gemayel's own position in trade for moves by the US to meet the above demands. ''Particularly, a politically weakened Gemayel,'' adds one veteran Western Syria-watcher.
Syria has always been careful not to endorse the all-out triumph of any of the rival factions next door - in the present case of Druze and Shiite forces - preferring instead something approximating a balance in which Syria holds the inescapable mediatory role.
Yet most foreign diplomats here are equally convinced that the Reagan administration is not, at least not yet, likely to countenance this kind of resolution.