WASHINGTON (AP) _ Doctors, hospitals, drug wholesalers and friendly neighborhood pharmacists are involved in a multimillion-dollar black market in prescription drugs that often are contaminated, misbranded or impotent, federal officials testified Thursday.

''This is terrible, this is sheer white-collar murder,'' said Rep. Thomas J. Bliley Jr., R-Va., at a hearing by the House Energy and Commerce investigations subcommittee on the illicit diversion of legitimate pharmaceuticals.

FBI official Hal N. Helterhoff and U.S. Attorney Larry D. Thompson of Atlanta said 48 individuals and three corporations, including doctors, druggists and pharmaceutical wholesalers or sales representatives in seven states, had agreed to plead guilty or no-contest to criminal charges stemming from black market drug activities.

In an 18-month federal undercover ''sting'' operation code-named ''Pharmoney,'' Helterhoff said, agents seized $600,000 in adulterated prescription drugs, including hundreds of thousands of tablets and capsules contained in plastic sandwich bags, bread wrappers, soft drink bottles and peanut butter jars.

Helterhoff and Thompson said racketeers, who are frequently college- educated businessmen, might order prescription drugs from manufacturers at little or no cost, perhaps by posing as a legitimate customer or a fictitious clinic.

Doctors and drug salesmen, lured by the promise of fat profits, sell free manufacturers' samples to black market agents, and pharmacists at non-profit hospitals or clinics deliberately overstock and sell excess drug supplies.

To avoid detection, the racketeers then repackage outdated drugs, sample medicines or stolen pharmaceuticals under unsanitary conditions, in garages or attics, and obliterate all ''sample'' markings, lot numbers, expiration dates, warning labels and other legally required markings.

The crudely packaged drugs then are ''peddled to the back door of neighborhood pharmacies'' for enormous cash profits, said Helterhoff, who sat at a witness table stacked high with recycled drugs in plastic bags and bottles.

The officials played a secretly recorded videotape that purported to show a racketeer bragging to a federal undercover agent that he $111,000 worth of black market prescription drugs in one week.

''It became apparent that this type of activity was not only criminal, but posed a danger to the health of the public who depend upon these medicines,'' said Helterhoff, chief of the white-collar crimes section of the FBI's criminal investigative division.

''The presence of diverted adulterated and misbranded drugs in the prescription drug distribution system is a national problem,'' Thompson said. ''At least one drug store in every city, town and village involved in the FBI investigation was found to be dispensing such medications.''

He said they included nearly every type of non-controlled prescription drugs, including blood pressure, heart and diabetes medications, thyroid pills, ulcer solutions, birth control pills and antibiotics.

''Some had been expired for over five years,'' Thompson said. ''The drugs that were not out of date when placed in plastic bags were often treated as if they had everlasting potency since the expiration date was no longer printed on the package.''

The sting operation, which ended in June but involves pending investigations against 40 other suspects, covered dozens of communities in Alabama, Georgia, Florida, Tennessee, California, New York and New Jersey, the officials said.