IF IT HAD any larger purpose, the bomb set off at the American Embassy in Beirut was presumably intended to intimidate the United States. This act of terror will almost certainly fail in that purpose. For despite a toll including a number of Americans and many Lebanese, the act was not a sign that everything is collapsing in Lebanon. The truth is that things are moving, though tentatively, the other way. Lebanon's president, Amin Gemayel, himself took office as the result of an equally hideous explosion that killed his predecessor, who was his brother; but under Amin Gemayel the Lebanese government is gradually extending its authority. Lebanon is not home free. But it would be wrong to concede the terrorists a victory they have not won.

The group that claimed responsibility for this murderous episode is described as a Shiite Moslem faction loyal to Ayatollah Khomeini in Iran. Tragically, Lebanon remains the kind of place that involuntarily hosts all too many bands of killers whose inspiration, support and loyalty are external. That is why it is so important to bring to an early and successful end the talks aimed at removing Israel's, Syria's and the PLO's remaining forces. Only in conditions in which the Beirut government is permitted to regain its sovereignty from foreign occupiers can Lebanon be expected to rise by degrees, with American and other international help, to the challenge of imposing domestic order.

One would not wish to say anything to detract from the courage and resiliency of the Lebanese, who have had to endure a breathtaking measure of regular and irregular violence for years. Still, the steadiness of the Americans in the embassy in Beirut and in other exposed places deserves respect. They live lives shadowed by the closeness of terror; some have died by it. The United States is fortunate to have in its service men and women who are prepared to take the considerable risks of representing their country in the unsettled quarters of the world.