As American Marines began a long-awaited withdrawal from Lebanon Tuesday, Israel again appeared to escalate its involvement in this divided country. While the Marines packed up, Israeli troops advanced northward from their southern Lebanon enclave to set up patrols near Damour, just 12 miles from Beirut. This was considered the most significant movement by the Israelis since they withdrew from that sector last September.
On the Lebanese political front, there was a flurry of activity as yet another formula was proposed to end the deadlock, this time apparently presented by Syria. But it failed to silence the thunder of artillery in the Shouf hills that overlook the Marine base at Beirut airport. Machine-gun, rocket, and mortar exchanges flared along the ''green line'' that divides Christian east Beirut from the Muslim west.
The fighting, together with the withdrawal of the Marines to the comparative safety of the Sixth Fleet after their 17-month stay, underscored the defeat of a US policy that had failed to:
* Secure an agreement for the pullout of 70,000 Syrian, Israeli, and Palestinian forces.
* Uphold Lebanese authority and sovereignty. The area under government control has shrunk from the capital and environs to only east Beirut.
* Rebuild the Lebanese Army, which fell apart faster this time than when it collapsed during the 1975-76 civil war.
* Establish a dialogue of reconciliation among the complex network of factions. The Muslims and Druzes are now more at odds with the Christians than ever.
Indeed, Lebanon is in a far more precarious state than when the US rushed in with political and military support after the Israeli invasion in June 1982.