Its title, "Fund for Assistance to FSN Employes of American Embassy Beirut," sounds like a subhead in a diplomatic cable. But behind the tongue-twisting bureaucratese is a spontaneous, worldwide effort by State Department employees to provide some extra financial help for the families of Lebanese employes of the United States killed or injured in the April 18 bombing of the U.S. Embassy in Beirut.

Half of the at least 60 persons who died in the explosion were what the trade calls FSNs or "foreign service nationals": citizens of other countries who are employed by U.S. overseas posts in jobs ranging from cooks and janitors to secretaries and translators.

As every foreign service officer knows, they are essential to the running of America's far-flung network of embassies and consulates. To show their appreciation and solidarity, officials in the department's Bureau of Near Eastern and South Asian Affairs banded together to raise a fund that the U.S. ambassador in Beirut, Robert Dillon, can use to supplement the regular benefits that will go to those who were injured or to the survivors of those who were killed.

Sheldon J. Krys, the bureau's executive director who has taken charge of the fund, said that contributions so far total about $25,000 "and we're just getting off the ground." What's more, Krys added, the effort has triggered an outpouring of support, not just from officers involved with the Middle East but also from other State Department people. Americans and foreign employees alike, in every corner of the world.

Even before they were aware that an official fund was being started, Chilean employes of the American Embassy in Santiago joined in sending one day's pay to their colleagues in Beirut. Since then, similar gestures have been made by the workers at at least 10 other overseas posts.

The American Foreign Service Association, which is the union representing foreign service personnel, and the organization of retired diplomatic and consular officers have chipped in with substantial contributions. But Krys probably is proudest of the son of one Middle-East country desk officer, who held a garage sale and chipped in the $40 he raised to the fund.

LAST SEEN WEARING PINSTRIPES? . . . If it's true that rats desert a sinking ship, the people charged with running U.S. foreign policy now have some not entirely welcome evidence that the ship of state is still seaworthy. At least, that's the looking-on-the-bright-side conclusion to draw from a two-page notice sent to all employes last week noting "reported obserations of rats" in the department's cafeteria.

The notice, entitled "Actions to Control Rodents in New State," caused considerable amusement among many employes who wondered why anyone, rats included, would want to eat in the cafeteria if they didn't have to. The notice didn't shed any light on that question, although it did point out proudly that "our cafeteria has recently been awarded a 'citation of merit' by the D.C. Health Department for consistently maintaining a high level of sanitation."

Still, the notice conceded, "the appearance of rodents in a building is an unpleasant and disquieting experience." And, in language that made clear the department expects everyone to do his duty, it exhorted employes to avoid eating at their desks, discarding food scraps in waste baskets and keeping nibbles such as cookies and candy in their desks.

"Remember, if you are not a part of the solution, you are a part of the problem," the notice said. And it served notice on the diplomats that in addition to such routine chores as negotiating with the Soviet Union, halting the spread of communism in Central America and bringing peace to the Middle East, "total cooperation of all employes in addition to the actions of responsible officials carrying out rodent control assignments must be marshaled."