IT'S LITTLE COMFORT to those cooling their heels in a doctor's waiting room right now, but a government commission says that soon there will be too many doctors in the house -- a surplus of 70,000 by 1990 and 145,000 by the year 2000. This word that the white coats are coming in big numbers does not necessarily spell relief for bill-payers, though; instead of good old-fashion competition, the result may be more doctors doing more work to more people for -- you guessed it -- more money. But there is one big change in the medical world that just might work to the customer's advantage in a doctor-glut situation: advertising.

This week, a federal appeals court upheld a ruling by the Federal Trade Commission that had ordered the American Medical Association to let its members advertise if they want to. This should inject some healthy competition into the profession, as even the AMA reluctantly acknowledged in mid-litigation this summer when it dropped its old ban on "soliciting patients." That amounted to a go-ahead for advertising, which dentists and lawyers already were doing.

Once patients and insurance companies -- consumers, if you will -- get used to this practice, doctors who advertise their fees won't be viewed as grubby or unprofessional. People aren't likely to see or swallow sleazy ads -- "Buy Two Shots, Get One Free," or "This Week Only: Your Choice of a Vegetable Slicer, a Clock Radio or an All-Expenses-Paid Trip to Hyattsville With Every Physical Checkup." What could result from safe and reasonable competition is a lowering of medical fees and a better chance for people to do some informed comparison shopping. There might even be some improvements in services; what about "Have Black Bag, Will Travel" for house calls?

We do confess to more than a passing interest in advertising, since it does support newspapers. But the potential benefit to be realized by the public in what may grow to be a buyer's market could be substantial. That's been the case with lawyers, certainly; prices of many routine legal services, from uncontested divorces to wills and house sales, have declined. When people don't know what the going rates are, they may be timed about asking -- and may even avoid medical or legal protection that they need and could afford. So just as it might even be good for business, it might shed new light on the mysterious and horrifying economics of medicine.