Major multinational pharmaceutical firms doing business in Central America have begun to tone down promotions of potent drugs to physicians by limiting claims of benefits while making fuller disclosure of risks.

This finding was made by Dr. Milton Silverman, a University of California drug specialist who compared what 15 golbal companies - American, Swiss and French - were telling Central American doctors in 1973 with what they began to tell them in 1976.

Silverman, who reviewed 26 widely used drugs; gave this summary of his findings:

For nine medicines, the manufacturers narrowed claims of effectiveness and strengthened the warnings to make them comparable to those they provide physicians in the United States, where the Food and Drug Administration requires proof of safety and effectiveness.

For two products, the producers were already making "reasonably full disclosure in 1973 and have continued to do so."

For 11 drugs, the companies "are continuing to exaggerate the clinical values of the drugs and to minimize, gloss over, or totally ignore the potentially serious of fatal side effects."

For four drugs, the problem by the expedient of not publishing anything in 1976 about them."

Probably the most dramatic change involved Chloromycetin, the Parke-Davis brand of an antibiotic, chloramphenicol, that causes a fatal blood disease in some users.

In the United States, the FDA has long required the Detroit firm to say in the official prescribing instructions and advertisements that chloramphenicol should not be used in "trivial infections," but should be restricted to a few serious or life-threatening diseases such as typhoid fever.

The labeling also warns of the link to the blood disease.

In Latin America in 1973, Silverman said, Parke-Davis was contradicting the advice it was giving in the United States by recommending Chloromycetin for disorders including tonsillitis, pharyngitis, eye and ear infections, abscesses and pneumonia. It did not disclose potential adverse reactions including the blood disease, nor give, the medical conditions in which the drug should not be used.

By 1976, however, Parke-Davis was telling Central American physicians virtually the same thing it was telling physicians here, Silverman said.

He based his findings on the 1973 and 1976 entries in the Central American Spanish-language edition of the "Dictionary of Pharmaceutical Specialities."

This is a widely used references volume that carriers entries exactly as companies want them and it is distributed annually to every doctor in Costa Rica, El Salvador, Guatemala, Honduras, Nicaragua and Panama, along with the Dominican Republic.

The 1976 edition was published Sept. 30, four months after the University of California Press published Silverman's book, "The Drugging of the Americas," and after the author testified before the Senate Select Small Business Monopoly Subcommittee.

The book and testimony were based on a first-hand survey by Silverman and two associates, who compared the labeling of 40 drugs provided by 23 international companies in the United States with the labeling they provided on the same products in 11 Latin American countries.

Although some companies defended the legality of overstating benefits and understating risks outside of the United States, Silverman testified that they were violating laws in four countries - Honduras, Panama, El Salvador and Colombia - that required full disclosure of hazards to physicians.

News reports on the Senate hearing were widely published in Latin America, Silverman said.

At the time, C. Joseph Stetler, president of the Pharmaceutical Manufacturers Association in Washington, acknowledged "the importance of the questions raised" in the hearing and said he intended to have them discussed by the International Federal of Pharmaceutical Manufactueres.

Three weeks laters, Stetler went before a meeting of the federation in London with an unprecedented proposal: to adopt a resolution calling upon the world's drug companies to adhere to standardized drug labeling and to make full disclosure of harzards.

Stetler said recently that he raised the issue in part because of the Senate hearing and, in an apparent reference to the publicity, "in part because of recurring concern expressed in various in other quarters."

The federation rejected Stetler's proposal, asking him instead to prepare a policy statement. As adopted by the federation at a meeting in November, the resolution said:

That labeling and entries in prescribing guides for a prescription drug "should be consistent with the body of scientific and medical evidence pertaining to that product, taking into account good medical practice and the requirements of each government's regulatory authorities."

That "particular care should be taken that essential information as to medical products' safety, contraindications and side effects is appropriately communicated."

That each of the more than 40 member associations "encourage compliance among its member companies with this proposal."

Silverman commented that the federation "unhappily . . . did not propose any method to implement the move." He said that a body such as the World Health Organization could "set up guidelines and maintain surveillance." He added:

"It remains to be seen whether the changes instituted by some global drug companies in Central America will be applied to all their products throughout the world, and whether their lead will be followed by other drug firms."