United States peace efforts in war-torn Lebanon have received a double blow. On Thursday, the 1,200-man US Marine contingent in Beirut was drawn further into Lebanon's interfactional fighting. After coming under brief attack at their positions near Beirut's international airport, the Marines and the USS Bowen returned fire against an artillery implacement thought to be manned by Druze militiamen.
It was the most serious retaliatory action to date by the US Marines, who are ordered not to fire unless directly attacked. It is also the first time the US Sixth Fleet ships off the Mediterranean coast have been activated.
The USS Bowen, a fast frigate, fired four salvos, and the Marines on the ground fired one. A salvo is six rounds. A Marines spokesman said later: ''We hit the target that we aimed at.''
The incident is likely to further escalate the already razor-sharp tension after five days of bitter fighting between the Druzes and the Christian Phalange militia in the Shouf mountains overlooking the capital.
On another front, Saudi Arabia announced after an emergency Cabinet session Wednesday that it was ''suspending'' its mediation in the Lebanese crisis ''until new positive signs emerge to enable Saudi Arabia to resume its peace efforts.''
The Kingdom is the only Arab state with sufficient leverage to be able to pressure the complex network of players into a truce. The US had been counting on the Saudis to use their influence to back up the mediation efforts of US trouble-shooter Robert McFarlane.
Mr. McFarlane spent two days in Damascus, conferring with President Hafez Assad and Druze leader Walid Jumblatt. Lebanese officials said the US special envoy had carried with him a framework to resolve the crisis. It included:
* An immediate cease-fire, followed by the deployment of the Lebanese Army in the Shouf and Aleih regions.
* Acceptance of ''red lines'' separating the militias and that there will be no further acts of provocation.
* A national dialogue of all major Muslim and Christian factions, followed by the formation of a national unity government.
* Agreement on revisions to the 1943 National Covenant that divides power among Lebanon's 17 religious sects.
But there were no signs of progress when McFarlane returned to Beirut on Thursday.
Indeed, the former White House official's only reported achievement was to win an agreement from Mr. Jumblatt Wednesday not to allow his militiamen to fire again on the 5,200-man peackeeping force from the US, France, Italy, and Britain.
After the four contingents came under fire, warplanes from the USS Eisenhower and the French aircraft carrier Foch on Wednesday flew over the Shouf in a show of strength and as a warning to Druzes.
But neither political nor military action was apparently sufficient to provide immunity for the peacekeepers. Three shells fell near the Marine positions the next day.