Beirut — In the aftermath of the US Embassy bombing last week, each country participating in the peacekeeping force is concerned about new attacks. The embassies of France, Britain, and Italy have been converted into virtual fortresses: Armored vehicles, troops, and sandbag barricades have been placed in front, with sharpshooters on rooftops.
Elsewhere in Beirut, the airlines, press agencies, and well-known businesses from countries represented in the peacekeeping force have either been given official protection or heightened their own security.
These moves underline the impression that Beirut, the only part of Lebanon free of rival foreign armies and where central authority has theoretically been restored, has begun to disintegrate again - with grave long-term implications for Lebanon and the countries now involved in helping it.
The tragedy of the US Embassy bombing reaches beyond the unfortunate victims. Faith in Lebanon's ability to recover from eight years of anarchy and civil strife was also among the casualties.
A saddened Western envoy suggested that, even if the US does eventually negotiate a withdrawal of 60,000 Syrian, Palestinian, and Israeli forces, it appears the prospects for permanent peace in Lebanon are limited due to rising internal tension.
That was underlined by renewed fighting last week in the Shouf region between Christian and Druze militias, marking a breakdown in the February ceasefire. At least 170 were killed in the previous round of clashes.
It is also reflected in the fact that many interest groups - political and religious - have begun again to establish their own forms of protection and self-rule, since no progress has been made in reasserting central authority in 80 percent of Lebanon.
The Islamic Struggle faction, which was one of three groups claiming responsibility for the embassy bombing, is the best example. An organization of fundamentalist Shiite Muslims, it has reportedly only ''come to strength'' recently with the help of Syrians and Iranian revolutionary guards who control eastern Lebanon.
Had foreign forces been withdrawn last year, it is doubtful that the small splinter group with loyalties to Iran's Ayatollah Khomeini would have received sufficient arms or training to be a threat. Islamic Struggle has also claimed responsibility for several of the attacks against the multinational peacekeeping troops since January.
As happened in the period following the 1975-76 Lebanese civil war, the euphoria about peace and reconciliation among the diverse and disparate factions in Lebanon appears to have been premature.
US confidence and credibility were also among the injured. The prestigious newsletter ''Middle East Reporter'' wrote:
''The Beirut blast may have driven home what had been apparent for a long time: that American initiatives, producing no tangible results after such a long time, were being overtaken by events. Whether the reaffirmation by President Reagan of his administration's Middle East commitment is sufficient to repair the serious damage already done is by no means certain.''
The timing of the embassy tragedy, just one week after King Hussein's decision not to enter peace talks with Israel, seemed to underline the feeling that the US was losing its grip on Middle East peace efforts.
This is in stark contrast to the situation in the aftermath of the Israeli invasion last year, when the US had a virtual diplomatic monopoly in the region. Both moderate and militant Arabs had turned to the US to sort out the conflict once and for all.
But seven months have passed since the end of hostilities and the return of the peacekeeping troops, putting into question the momentum and psychology of peace. In an editorial released Sunday, Beirut's ''Monday Morning'' magazine warned:
''Despair and disunity are good bedfellows, and when loss of hope sets in, loss of allegiance is usually around the corner. . . . It will take hard evidence that Washington's commitments are not a PR man's idea of morale-raisers but a prelude to action.
''America has been promising quick action towards a free and stable Lebanon since last September, but has done little to show that its commitment to a free and stable Lebanon is stronger that its commitment to a belligerent and expansionist Israel. . . . Hope does not spring eternal in the Lebanese breast.''
US credibility in the eyes of its allies, particularly its partners in the multinational peacekeeping force, was also damaged. Even before the blast, Italy had hinted that its contingent of 2,000 troops might be withdrawn if no progress was made in negotiations. Now that its diplomatic staff in Lebanon lives like an embattled species, the issue will not be any more popular at home.
''Allies are abundant at times of success. But they usually evaporate when they begin to sniff failure,'' an envoy noted.
Britain, France, and Italy all have too great a stake in the Arab world to jeopardize relations through long-term association with a US diplomatic failure in the region - and the accompanying physical dangers.
While the rescue mission at the bomb-shattered embassy has now entered its final phase, it will be a long time before the political toll can be fully assessed.