THE FEDERAL Emergency Management Agency has rejected a recommendation from the Lawrence Livermore National Laboratory that factory workers protect themselves from nuclear attack by jumping into large pools of water wearing "as much clothing as possible." The idea, says the agency, is "ludicrous" and likely to "undercut the entire civil defense program and cause loss of validity to the very real concept of nuclear survivability." Why would the agency think that?

We would be insincere in denying that the thought of thousands of well-wrapped workers bobbing up and down in the factory swimming pool has its humorous aspect. And we're not sure that, despite its many years of work with things nuclear, the Livermore Lab has thought through all the angles of its proposed remedy. What if the workers don't want to wear their entire wardrobes to work each day? Will they have time to hurry home for another layer or two?

The report also suggests "diving about four feet down and spending as little time as possible at the surface for air." That should be easy if you're wearing long underwear, three sweaters, two winter coats and a muffler. The difficulty we foresee is getting to the surface at all. And we take no comfort from the report's suggestion that workers "taking advantage of large bodies of water should not only be good swimmers . . . they should also tether themselves to a flotation device." How many bodies of water do you know of that come equipped with hundreds of conveniently spaced "flotation devices." Lobster buoys, perhaps?

Who will be there to blow the whistle that tells the sodden workers that it's time to get out of the pool and go back to the locker room? Perhaps their supervisors will have shielded themselves from blast and fallout by wrapping themselves in the "wet, opaque blankets" that the report also recommends.

Still, we wonder why FEMA has become so thinskinned. This, after all, is the agency which, less than a year ago, revealed the good news that, given the relative survivability of livestock and people, food supplies would be no problem in the post-nuclear environment. And the same one that, only a year earlier, unveiled a sure-fire plan to evacuate two- thirds of the population to rural areas -- a plan that depended for its success only on the Soviet's assuring us of at least one week's warning before attack. Why so sensitive all of a sudden?

It also seems to us that, in canceling the remainder of its study grant, FEMA has been insensitive to the real difficulties that Livermore faced. After all, its charter called for developing a plan to save city factory workers in the event of nuclear attack. Maybe it isn't so easy to develop such a plan without seeming, well, ludicrous.