The nation's major drug manufacturers filed suit yesterday to block the government from encouraging doctors and pharmacies to fill prescriptions with cheaper, so-called generic equivalents of brand-name drugs.

The Pharmaceutical Manufacturers Association charged in a suit filed in U.S. District Court in Baltimore that publication of a guide to wholesale drug prices and a list of supposedly equivalent drugs would mislead the public, physicians and pharmacists.

The price list is due to be published next month by the Department of Health, Education and Welfare, and a separate list of "therapeutically equivalent" drugs is being compiled by the Food and Drug Administration. Drafts of both lists have been prepared.

The suit also alleges that the government has been engaged in an "overall program of officially favoring, fostering and assisting manufacturers of cheaply priced, lower-quality imitative drug products, to the detriment of competing firms that carry the burden of research and development of innovative therapuetic drug entities."

The manufacturers asked the court to stop the government from:

Encouraging government agencies to buy so-called generic drugs, that do not have to meet as rigorous application requirements, even where the law requires the agency to buy the more-thoroughly-tested products.

Making it harder for physicians to write Medicare and Medicaid prescriptions for brand-name drugs where generic drugs exist by putting a price limit for certain prescriptions.

Lobbying state agencies and legislatures to adopt laws encourageing substitution of cheaper generic equivalents.

A spokesman for the Department of Health, Education and Welfare said agency officials had not had time to study the suit and would have no comment.

The drug manufacturers claim that publication of the new price lists would cost them money, as doctors would be encouraged by official government lists to write prescriptions for cheaper imitative drugs, diverting income from the research-oriented drug companies.

The pharmaceutical companies did not seek a temporary restraining order in the suit because publication of neither the price list nor the list of equivalent drugs is imminent.

The major pharmaceutical companies contend that copies of products do not have to meet the same rigorous testing procedures as to efficacy and therapeutic value as the original products do in a "new application" procedure.

All drugs do have to meet minimum production standards.

But, the major drug manufacturers contend, simply because a drug has the same amount of active chemicals as a brand-name drug does not mean that the body absorbs it as fast or as safely as the brand-name drug.

In the case of aspirin, for example, one product may dissolve quickly in the stomach while another may lodge for awhile, although both tablets qualify as aspirin because they contain the same amount of acetylsalicylic acid.

The tablet materials in which the aspirin is contained may differ, as well as the shape of the aspirin granules themselves or the tightness of the tablet, the suite claims.

Studies have shown that there is more gastrointestinal bleeding caused by some cheaper aspirin tablets that lodge against the stomach wall and take longer to dissolve.

"The manufacturers have a case, although it is probably exaggerated," said one leading physician. "In many cases, such as with digitalis (used in congestive heart failure), it makes a difference how much and how fast the drug is absorbed and available in the body."

The drug manufacturers also charge that publication of wholesale prices of drugs would be misleading, in part because invoice prices often have little relationship to the actual prices drugs sell for and in part because prices change rapidly.

The draft price list prepared by HEW contained many outdated prices, the suit said.

The drug manufacturers said they offered to cooperate with HEW in producing a more "meaningful" price list that would reflect retail prices of drugs.