Surgeon General C. Everett Koop has backed off from a controversial effort to force 34 of the most senior scientists and administrators at the National Institutes of Health to retire because they have served for more than 30 years, officials said yesterday.

The policy had created a furor at NIH. But Koop's acting chief of staff, Dr. Edward Martin, said yesterday that 12 of 14 laboratory chiefs and scientists scheduled for retirement this year will be given a year's exemption from the mandatory retirement rules.

Koop was attempting to enforce the military's "30 and out" rules for the first time because the commissioned officer corps of the Public Health Service has an "excess" of senior officers, reducing promotional opportunities for younger members. Koop also has proposed that officers exchange their khakis for uniforms as a symbol of commitment to the corps' mission as "the nation's only defense against nonmilitary disaster."

Critics say Koop's order would have eliminated some of the best scientists and administrators at NIH, if not directly by forcible retirement, then indirectly because they were fed up with such treatment.

"I have reviewed the list" of officers notified of mandatory retirement, said a leading scientist familiar with NIH. "Some of the very best scientists in the world are on it. It is the most illogical management decision I have ever seen."

Officers with 30 or more years of service received memoranda on May 29 that began with the phrase: "Attached is INSTRUCTION 3, subchapter CC23.8, 'Retirement of an Officer with 30 Years of Active Service,' which was recently approved by the Surgeon General."

Koop said in the letter that an agency head may "request the retention" of up to five individuals -- 15 percent of those who received the letters -- at NIH.

But after the resulting ferment, Martin said last night that "we have no intention of forcing senior scientists to leave NIH."

Decisions on officers scheduled for retirement in 1988 will be made by July 15, Martin said, and the result for those 20 individuals is likely to be the same.

Dr. Kenneth Spring, an NIH physiologist who is a civil servant and not affected by the retirement rules, said the letter had a "destabilizing" effect on NIH. "A lot of people can triple their salaries by leaving and they have lost their feeling of security. They are already looking," he said.

"Although Koop is popular now, he has a fantasy of a crack assault team that would move every three or four years, attacking acne one year, AIDS the next. This is scary for us in the trenches," Spring said.

But Dr. Cecil Fox, a commissioned officer who did not receive a mandatory retirement letter, said he wholeheartedly supports Koop. "This is not a uniformed country club for physicians and scientists to do what they wish for as long as they want," he said.

"I know that when I joined the Public Health Service all this was explained to me," he said.

Among those who received the form is Dr. Saul Rosen, deputy director of the clinical center at NIH. Rosen was promoted to his position three years ago and is the highly regarded No. 2 officer in charge of the 600-bed research hospital at NIH.

Rosen, whose name was obtained from a computerized seniority roster, confirmed that he had received a letter, but declined to comment on grounds that any remarks would seem self-serving.

Dr. William J. Zukel, deputy director of the division of heart and vascular diseases in the National Heart, Lung and Blood Institute, also acknowledged that he had received a letter. Zukel is the recipient of the distinguished and meritorious service medals, the highest and second highest awards in the corps.

Doctors appearing on a computerized list of officials subject to mandatory retirement have been reluctant to discuss the matter. Koop has been unsympathetic toward officers seeking "preferential treatment," as he put it in a video disseminated by the Commissioned Officers Association of the U.S. Public Health Service.

According to the list, lab or branch chiefs were asked to retire in the National Cancer Institute, the National Heart, Lung and Blood Institute, the National Institute of Allergy and Infectious Diseases, the National Institute of Arthritis, Diabetes, Digestive and Kidney Diseases, and other labs.

In explaining his actions, Koop said he believed that without a major revitalization the health service corps would be eliminated within 10 years. It has come under harsh attack from the Office of Management and Budget, the secretary of the Department of Health and Human Services and members of various armed forces as falling short of its mission of providing an expert, flexible and mobile force.

Koop, who is regarded as something of a hero within the corps for making public health his only consideration in handling the AIDS crisis, has called for revitalizing the corps by wearing uniforms, rotating tours of duty and by enforcing retirement provisions.

Public health officers facing retirement this year entered the corps before 1958. Many of them started at NIH as research associates. When they became eligible for tenure, they chose between the commissioned corps and the civil service. The Public Health Service paid as much as $12,000 more, Martin said yesterday.

A senior public health official said, "You take the very best people, those who decided not to be bureaucrats but to stay in the lab and run a scientific group and they're told they've got to retire. It's not that easy to work in the government. It needs the best people it can get. This is ruining it."