The country's most widely prescribed drug, the tranquilizer and muscle relaxer Valium, can interfere with one of the body's key mechanisms in renewing itself, a University of Califoria scientist said yesterday.

He based his conclusion on a demonstration that the drug can inhibit muscle cell renewal in chick embryo cells. He has done no studies on animals or humans.

Authorities differed sharply on whether his findings are significant, and research officials at Hoffman-La Roche, Valium's maker, said they see no meaning for humans in the research.

But the scientist, Dr. Richard C. Strohman, said, "Out work should at least be a warning to people using the drug."

"I'd be most concerned about people who use it over a long period," he added. "Say, months or perhaps even weeks I'm just saying that if I were taking it and this effect had been shown, I'd think twice."

Strohman is a cell biologist and director of the University of California at Berkeley's Health and Medical Sciences Program, a training project for doctors and other health workers.

American doctors last year wrote more than 57 million prescriptions for Valium. The National Institute on Drug Abuse has estimated that one adult in nine is currently using a tranquilizer, with Valium by far the leader.

It is also one of the drugs that has been used by former First Lady Betty Ford, who last month committed herself to medical treament for combined prescription drug and alcohol addiction.

Strohman, Everett Bandman and Charles Walker exposed fresh chick embryo cells to various - mainly high - Valium concentrations and found that the drug "is decidedly disruptive" of normal muscle formation and that "it inhibits synthesis of muscle cell protein." A report of their work is carried in the May 5 issue of the journal Science.

The body's cells, including muscle cells, constantly renew and replace themselves, and Strohman said any adverse effect could apply to adults as well as unborn, developing fetuses whose mothers use Valium.

He said fresh chick embryo cells are much the same as human cells for the purpose of establishing such effects.