A powerful antibiotic that occasionally causes fatal anemia was prescribed 248,000 times by American doctors last year, despite expert agreement that it should seldom, if ever, be used in office practice.

The potent but treacherous antibitic is chloramphenicol, sometimes known by the trade name, Chloromycetin.

In the late 1950s and early 1960s prescriptions for it were written by the millions. But doctors began to realize that once in 20,000 to 40,000 cases it caused aplastic anemia.

This blood disease is usually fatal. When it is not, it keeps its victims sick and hospitalized for long periods. Sometimes they develop leukemia.

Congressional drug investigators-notably the late Sen. Estes Kefauver (D-Tenn.) and, in recent years, Sen. Gaylord Nelson (D-Wis.) - have held days of hearings on the chloramphenicol problem and the reports of some of its victims.

As a result, Nelson reported last week, 1978 chloramphenicol production was 6.2 million grams (or 24.8 million doses) compared with 45.7 million grams in 1967.*tNine-tenths of use of the drug now is in hospitals, where there are some legitimate applications in serious illnesses - typhoid, severe salmonellosis and rickettsial infections, for example.

As long ago as 1969, however, Dr. Paul Wehrle of Los Angeles County-University of Sourthern California Medical Center testified that the drug's nationwide use should be no more than 2 million grams yearly. This would be only a third of the 1978 use.

As for by the office-based doctors who wrote the 248,000 prescriptions last year, virtually all is unjustified, according to a January 1979 article by Dr. William Schaffner, Wayne Ray and Dr. Charles Federspiel of Vanderbilt University.

Use of the drug by office practitioners has dropped. There were 366,000 prescriptions for it in 1976, then 321,000 in 1977.

But Schaffner, Ray and Federspiel wrote in the Quality Review Bulletin, a publication of the Joint Commission on Accreditation of Hospitals, that the drug is oftern used still in "relatively minor infections . . . best treated with less hazardous antibiotics."

"There are virtually no indications for use of Chloromycetin in out-patient, office practice today," Schaffner said in an interview. "The people in our university practice don't use it, and I have a lot of friends in private practice who don't use it."

Who does use it?" "Physicians who have isolated themselves from advances in medicine," he replied. "Don't forget, the incidence of aplastic anemia is so small that a doctor may use the drug a great deal and sincerely tell you he 'never' sees an adverse reaction.

"From a nationwide public health standpoint, however" - as well as the standpoint of the patients with the reactions - "the adverse reactions are a serious problem," Schaffner said.