A cholesterol-lowering drug taken mainly by middle-aged men here and abroad in hopes of preventing heart attacks is being banned by West Germany on the basis of a massive new study of serious and sometimes fatal side effects.

American physicians prescribe the drug, clofibrate, for an estimated 450,000 men and 290,000 women. The trade name used in this country is Atromid-S.

One of the study's major findings was that long-term clofibrate users did not have fewer fatal heart attacks same time, however, the users had a sharply higher rate of deaths from cancer and other diseases, principally of the liver, gall bladder and small and large intestines.

Applied to American men who use clofibrate, the finding raises the possibility of hundreds of avoidable deaths a year.But the reliability of the finding is sharp dispute, partly because it doesn't take into account age difference among participants in the study.

When adjusted for age, the difference in the user and nonuser fatality rates doesn't attain statistical significance, according to some scientists and Ayerst Laboratories, which is licensed by Imperial Chemical Industries (ICI) of Great Britain to supply clofibrate in the United States.

But other scientist who have reviewed the study emphasize that among users, deaths from causes other than heart attacks occurred at a 35 percent higher rate than among nonusers.

In Washington, a spokesman for the Food andDrug Administration said that the FDA has begun an evaluation of the study and has asked Ayerst to submit slides of livers of rodents that developed cancer on Atromid-S. The significance of the rodent data is uncertain.

In May 1977, National Institutes of Health scientists reported a finding that gall bladder disease occurs 54 percent more often in clofibrate users than in nonusers (a World Health Organization study found a rate nearly 2 1/2 times higher).

On the basis of the NIH report, a petition to FDA to remove Atromid-S from the market was filed by the Health Research Group, a unit of Ralph Nader's Public Citizen, Inc. HRG director Sidney M. Wolfe said last night that he will renew the petition.

The study was a cooperative venture of the World Health Organization (WHO) and ICI. It enlisted 15,745 healthy men-who hadn't had heart attacks-in Edinburgh, Budapest and Prague. The study lasted 13 years, ending in late 1976. The results were reported last month in the British Heart Journal.

The men were divided into two main groups: Those with high levels of cholesterol in their blood who got clofibrate, and those who also had high serum cholesterol levels but who got dummy pills, or placebos.

Although use of the drug apparently didn't attacks, users had a rate of nonfatal attacks 20 percent lower than nonusers. Among users who smoked or had high blood pressure, the reduction was still lower.

"What is clear at last is that reduction of serum cholesterol concentrations is relevant to the prevention of coronary heart disease," one of the study's authors, Dr. M. F. Oliver of Edinburgh, Has said.

Such a reduction sometimes is obtained by diet and other nondrug measures. In the FDA-approved labeling for Atromid-S, which entered the U.S. market in 1967, Ayerst recommends the drug as an adjunct to such measures.

The West German ban takes effect Jan. 15 and applies to 24 companies that sell drugs containing clofibrate. ICI says it will protest the ban as medically unjustifiable and is considering legal action against the West German government.

In an editorial last month, Lancet, a leading medical journal published in Britain, said that taken together with the NIH gall bladder finding, the WHO report "should spell the end of clofibrate, except maybe in the desperate problem of gross hypercholestermia [extremely high cholesterol level]."