The days of snake oil salesmen may be over, but promoters of quack medication and cures still have a booming, multimillion-dollar business in this country.

And while Food and Drug Administration officials express concern about the problem, they are the first to admit that they have trouble coming to grips with it.

FDA Commissioner Arthur Hull Hayes Jr. said in a recent speech to the Pharmaceutical Advertising Council that his agency had been "simply overmatched . . . . There are too many quacks, too skillful at the quick change of address and product name, for the cumbersome procedures of FDA."

"There is no question that there is more we could do to stop quackery," explained FDA spokesman Bruce Brown, "but it boils down to a question of resources" and whether employes should be diverted from other tasks.

The FDA defines quackery as any drug, food or mechanical device that is promoted through unfounded or exaggerated health claims that are not supported by scientific data. FDA officials said today's products appeal to the same kinds of customers as the quackery products of the past--they either want to be cured or made beautiful.

Now, agency officials said, such products include body wraps to reduce weight, electric muscle stimulators to tone up the body, electronic hair-growing devices and creams that promise to increase bust size. The FDA also considers many fad diets to be a form of quackery.

The agency used to do more to fight the problem. But about 20 years ago, the effort began to decline, according to Paul Sage, a consumer safety officer.

First the FDA lost several expensive and well-publicized quackery cases in the late 1950s. Shortly after that, Congress amended the Food, Drug and Cosmetic Act to tighten control over prescription drugs and new drug products.

It ordered FDA to begin checking effectiveness of all new drugs before they entered the marketplace and to review all drugs that had been introduced since 1938. "We're still working on that task," said Sage.

At first, Sage said, promoters of quack medical products did not realize that the agency had cut back enforcement efforts, but now they do. The result is an increase in worthless products.

A major problem is that quackery cases are expensive and difficult to prosecute, Brown said. By the time the agency proves that a drug or cancer cure, one of the most common types of quackery, will not work, the inventors already have pocketed the profits and invented another "cure."

The FDA has developed a priority list for deciding which cases to go after. The agency will assign investigators to cases involving products that could hurt consumers and are widely advertised or cases involving major economic fraud. But if the fraud is not major or considered dangerous, FDA sends a "talk paper" to its 32 regional offices for release to consumer and business groups and to the media.

In 1982, FDA seized 64 products, issued an injunction to stop production of another and confiscated 1,953 items that were being imported into the country, Brown said. The agency also works closely with the Consumer Product Safety Commission and with the U.S. Postal Service in cases involving mail order fraud. The cases can be controversial, and political.

For instance, the FDA lists immuno-augmentative therapy as a quack cancer treatment because the zoologist in the Bahamas who invented it has refused to provide the agency with scientific proof that it works.

The therapy involves concocting a serum from a patient's blood and then reinjecting it into the bloodstream to increase immunity to cancer. Despite the FDA's warnings, state legislatures in Oklahoma and Florida recently approved the sale of immuno-augmentative therapy devices in those states after intense lobbying by those who believe in the treatment.