Antarctic krill, the shrimplike crustaceans once touted as a virtually inexhaustible source of food for the world, may never fulfill their promise, according to marine biologists from the University of California at Santa Barbara.

Krill, they found, are not nearly as plentiful in the wild as once thought and the current comparatively low volume of krill fishing may be depleting the population.

Just a few years ago experts forecast that krill could supply up to 150 million tons of high-quality protein per year, more than double the total amount of seafood harvested worldwide. Now, it looks as if the current krill harvest, a modest 1 million tons a year (mainly by Warsaw Pact countries and Japan) may not be sustainable. The Soviet catch has fallen to one-quarter of what it was three years ago.

New studies of the life of the two- to three-inch-long animals shows that their huge schools are not distributed uniformly and that their reproduction is about half as prolific as once thought. Also, the main fishing season, the Antarctic summer, is also the breeding season. This means krill trawlers have an unusually severe impact on the species' reproductive potential.

These findings, by Robin M. Ross and Langdon B. Quentin, are reported in the current issue of the journal Bioscience.