SO MANY have been lost to war and terror in Lebanon, and so bleak is the vista that stretches ahead for the Lebanese, that it may seem almost indulgent to turn for a moment to the plight of a handful of Americans in Beirut. Yet our attention is caught by a couple of anonymous phone calls made recently to Western news agencies in that broken city. In the first call, last week, someone claiming to speak for the terrorist organization known as Islamic Jihad, or Islamic Holy War, said the group was holding five Americans who have disappeared in predominantly Moslem west Beirut since last March. The caller said the five were in good condition and would be released unharmed if all Americans leave Lebanon.

In a second call this week, made after the State Department had declined to yield to this implicit threat, the tone changed. For the first time, the five were identified by name, and a specific action was threatened against them: they are to be tried as accused agents of the CIA. "They have exploited the hospitality accorded to them by Islamic areas to persist in their subversive activities and will get the punishment they deserve," the Islamic Jihad spokesman said. Meanwhile, he claimed responsibility for the death of "two French spies" -- the two French military observers who, wearing white helmets and armed only with pistols, were ambushed while patrolling a Moslem suburb of Beirut on Monday.

Islamic Jihad has previously, eagerly, taken responsibility for conspicuous acts of mass vengeance in Beirut and elsewhere. Its credibility as a murderous enforcer of its anti-Western passions is not in the slightest doubt. Who does not wonder, however, at the moral cowardice of an organization that would threaten five worthy people who either were serving Lebanon faithfully and selflessly or who are members of professions traditionally enjoying immunity from local strife?

Jeremy Levin of Cable News Network was kidnapped last March 7. William Buckley, an American Embassy political officer, was abducted on March 16. The Rev. Benjamin Weir, a Presbyterian minister, and Peter Kilburn, an elderly librarian at the American University of Beirut, disappeared on Dec. 3. The Rev. Lawrence Martin Jenco, Beirut director of Catholic Relief Services, was kidnapped just last week. Their countrymen, who cannot reach them, reach out to them.