Sen. John Melcher, from a state with more cows than people, roused some of the latter recently when word drifted back to Montana that he had foresworn dining on those cows. But the word was wrong. A Washington magazine misreported that Melcher was a vegetarian. That was close enough, at least typographically. The senator is a veterinarian.

A Los Angeles newspaper picked up the vegetarian story, and soon the breezes blew it north and west and into astonished ears from Missola to Billings. Melcher began hearing from ranchers and cattlemen, who didn't put him in office to go East to sup on pita bread and celery stalks. Stay calm, Melcher reassured the he-men down at the corral, it's just another media foul-up. Remembering what happened to Fred Harris of Oklahoma when he apostacized from the true faith of oil, Melcher quickly sent out pictures of himself happily ravishing one of Montana's juiciest cows.

That would appear to end the matter, with Melcher's career safe and his palate savoring the 160 pounds of beef that is the per capita consumption in America.

But a case can be made that Melcher panicked too soon, as freshmen senators tend to do. With a little reflection, a strategy was available that would not only have enhanced his career but also livened his stay in Washington, as dull as it must be for a man used to roaming the range healing creatures great and small.

The enhancement would have been sure to come had Melcher really gone vegetarian - for, say, a year. Then, shedding the tears of the prodigal, not to mention speaking in the new tongues of the born-again. Melcher could have announced that he had gone back to meat eating. Voters warm to one of the fallen who rises again. A few years ago, an eastern senator bolstered his campaign by announcing that he was a recovered alcoholic. He went on to trounce his opponent, being perceived by the voters not as an ex-lush but as a strong-willed battler whom the state needed to bring sobriety to Washington.

Melcher, a senator for less than a year, could have afforded to take the risk of vegetarianism for a brief spell. The next time in the polls, Montanans would have remembered less his lapse than his recovery.

By then, Melcher would also be a best-selling author, his outside income as a veterinarian made irrelvant by royalties from "Doctor Melcher's Congressional Meat Diet." Doctor, that magic word, as Drs. Atkins, Reuben, Solomon and Stillman know, assures success in dietology. Melcher's main risk in all this would have been not with the voters but with the pleasures of the vegetarian way. What it he discovered, as have countless others, that vegetables, fruits and grains make a diet that is healthy, economical and ethical?

The second enhancement would bave been to the senator's ego. During his year as a vegetarian, Melcher would have been the darlings of Washington's hostesses. Of late, darling are hared to come by now that the Georgians have made the rounds and hostesses have learned that grits are better used for caulking the water pipes than eating. Having a vegetarian to dinner is one of the few challenges left for the hostess who has seen them all. Vegetarians used to go to Washington dinners and say nothing about their cautious ways. Adopting the manner of St. Francis among the publicans, they would eat what was served but not ask for seconds. But a few pathfinding vegetarians began calling ahead, asking the hostesses to put aside a little broccoli, squash and wheat germ and that would be plenty.

Now when a vegetarian calls ahead, he is likely to be told not to worry, that only last week Andy-Jacobs came to dinner and things went well. Jacobs is the Indianapolis congressman who is a passionate vegetarian, with neither his career, much less his health, suffering. The message is clear: Anyone can cook for the meat-eater, but only the imaginative and brave hostess can satisfy an Andy Jacobs.

But where can more Andys be found if even a senator with re-election five years away grows nervous at the sound of lettuce crunching in his own mouth?

Vegetarians are lionized at dinner parties not because hostesses can reveal their kitchen nimbleness but because no better time exists to theorize about food than when eating it. Ordinary clods who are vegetarians become cosmic philosophers when table partners ask about the mysteries of grape nuts. Vegetables have replaced living together, Arabs and running as enchantments to be "into." Vegetarians can quote their own, such as Shelley or Shaw. The latter, who lived into his 90s, regularly enlivened dinner partners by referring to the meat on his neighbors' plates as the corpses of fellow creatures.

So now John Melcher is back to being one of the pack, a herd member of Congress as anonymous as the cows back at the Lazy B. His chance to live a little - to get the DES out of his system and the adulation of Washington hostesses into it - is gone. He is sending out picutres of himself salivating before steaks.

But even the pictures are risky. What is Melcher doing, if not eating vegetarians? Montana's cattle are hale advertisers of the vegetarian way, because what do they eat but 25 pounds a day of grasses and grains, consuming the same kind of vitamins of the classic vegetarian diet beloved by Shelley, Shaw and the darlings whom Washington hostesses flight among themselves to have in next Friday night.