SO LONG cellulite, farewell flab. Thursday's headline was enough to brighten even tax day and surely must have produced a run on Baskin- Robbins. The news that gratified gluttons everywhere is that American industry is winning another Battle of the Bulge. Scientists at three different drug companies report significant progress in the development of a pill that will melt fat. The mind boggles. The mouth waters.

Pharmaceutical manufacturers caution that development of this chemical substitute for will power is in the early stages and must, of course, win approval from the FDA before it can be marketed. There may be side effects, too. But who wouldn't tolerate a slight fever to achieve a slim figure? Or endure a little dizziness in exchange for a dozen doughnuts?

Befores ten of millions of Americans begin popping pudge preventers with their morning malteds, however, we should give thoughful consideration to certain esthetic, ethical and economic questions. First, do we all really want to look like Cheryl Tiegs and Christopher Reeve? Of course we do. Next question.

Isn't there something vaguely wrong about getting away with gluttony? Will the national Puritan conscience--or what's left of it--be offended if overeaters stay svelte? Perhaps Mother Nature will punish our presumption by causing the drug to recreate us in even stranger shapes. Fortunately, there is still time to work on revising attitudes and eliminating any communal tendency to expect retribution for sin. A few marathon TV talk shows should do the trick.

Finally, we must prepare for economic upheaval. Fat is big business in this country, and there are hefty profits in heavyweights. The Weight Watchers empire can be expected to strike back. The saccharin lobby will weigh in with arguments against the pill. The diet drink industry won't go quietly down the drain. If jobs are to be preserved, adjustments will have to be made. Assets should be redirected into cocoa futures and pork bellies, for bellies will surely be up. Weight reduction counselors should be retrained so that a work force skilled in clothing alteration will be available. And the energies of the diet food manufacturers can be directed toward deep frying and whipped cream.

An army of the obese is rooting for the miracle men of Eli Lilly, Burroughs Wellcome and Hoffmann-LaRoche. Spoons in hand, hot fudge at the ready, millions wait for the word to dig right in without fear of fat.