The chief of the Food and Drug Adminstration estimates that elimination of unnecessary X-ray examinations could reduce the costs of health care by up to $2 billion a year.

Commissioner Donald Kennedy said that an estimated 30 per cent of all diagnostic X-rays aren't needed, but are ordered out of "concern about professional and medico-legal consequences of failure."

In 1977, Americans will have 241 million X-rays costing $6.3 billion.

The government centers responsibility for curbing needles radiation exposure - particularly from medical and consumer products - in the FDA's Bureau of Radiological Health.

Kennedy praised bureau director John C. Villforth for undertaking studies to show that X-ray exposures can be reduced sharply.

The commissioner cited a pilot project in a large hospital where clearer emergency-room guidelines for skill X-rays for possible trauma reduced orders for them 40 per cent.

On a national basis, this alone would decrease radiology costs by $53 million a year, Kennedy told a reporter.

He said that over and above the $2 billion figure is a potential for an additional short-term saving of nearly $150 million a year merely on film and materials for diagnostic X-rays that now are repeated - but could be eliminated by improvements in quality assurance. Labor savings would raise the $150 million estimate "considerably higher," Kennedy said.

X-rays are hazardous to a small proportion of the persons exposed to them. For that reason, needless or excessive exposure, in addition to being wasteful, creates avoidable health problems, particularly radiation-induced genetic defects and cancer.

Kennedy said physicians and technicians could halve the total genetic radiation dose simply by limiting the X-ray beam to the proper size and by shielding the gonads of male patients.

On the basis of National Academy of Sciences estimates, he said that this step alone, by decreasing genetic defects in future generations, ultimately could reduce health costs by about $750 million annually. This possible deferred saving would be in addition to the $2 billion.

The fetus is particularly sensitive to radiation-induced cancer. To make physicians more aware of the need to consider the pregnancy status of women patients of child-bearing age before ordering abdominal Z-rays, the bureau has set up a special program.

Three years ago, the bureau upgraded the capability and quality of diagnostic X-ray equipment by setting a performance standard.

In addition, the bureau has worked with several state and local agencies to weed out poor techniques, such as failure to use shields and use of excessively large X-ray beams. One project operating in 28 states has achieved a 40 per cent reduction in patient exposure to dental X-rays.

But "inadequate X-ray equipment and poor techniques" continue to be a "major source" of avoidable waste and hazards, Kennedy said. "Much more remains to be done."

Kennedy focused on the X-ray issue during a wide-ranging interview in his downtown office last week.

During his eight months in office, he has been occupied with the furors set off on Capitol Hill and around the country by the agency's efforts to eliminate saccharin from soft drinks (because the artificial sweetener, in Canadian and other studies, caused cancer in mice), and to block efforts to legalize Laetrile for cancer patients (mainly because it hasn't been proved effective and displaces "forms of therapy that have some chance of providing real medical benefits").

Kennedy fears that the main political result of the saccharin uproar probably will be "a significant attack" on consumer protection laws that govern the cancer-causing chemicals blamed by scientists for 60 to 90 per cent of all cancers.

"Our social role is simple," the commissioner told the Academy of Medicine in a recent speech. "We are the messengers who bring the bad news, and Congress is the King who beheads us in return."

Advocates of the legalization of laetrile - who have won their battle in a dozen states - have emphasized "freedom of choice," defined as the right to choose one's own medicine even if it hasn't been proved to be effective.

Kennedy says it is "no accident that this argument has a strong appeal to the political right."

The Laetrile furor has fueled support of a bill to repeal the 1962 drug laws that required pharmaceutical manufacturers, for the first time, to provide substantial evidence of effectiveness as well as safety. The bill, introduced by Rep. Steven D. Symms (R-Idaho) now has more than 100 co-sponsors. Another long-time advocate of repeal is Milton Friedman, Nobel Prize-winning economist and columnist.

In the interview, Kennedy said, "You don't have free choices unless they're informed choices" - a view consistent with the premise of a classical free market that transactions occur between fullp informed buyers and fully informed sellers.

The commissioner said that "probably the best," example to make his point is DES, the sex hormone that physicians began prescribing in the 1940s to prevent threatened miscarriages. No substantial evidence of DES effectiveness ever has been produced.

In 1971, researchers found that DES caused sometimes fatal vaginal cancer - not in the women who took the drug on the women who took the drug on the advice of their physicians, but in their teenage and adult daughters. More recently, scientists have found evidence of sterility in male offspring of DES mothers.

"The risk was too heavily deferred" - for 25 years or even longer, in some cases - and was transferred by the consumer to another person, Kennedy said in arguing that the choice to take DES wasn't "free."

Advocates of repeal of the effectiveness requirement also have charged that it has caused a "drug lag," causing a slower rate of introduction of valuable new medicines in the United States than elsewhere. Kennedy denied the charge.

Saying repeal "would project us into a therapeutic stone age", he cited a class of heart disease drugs called beta-blockers, several of which were introduced abroad. In FDA-ordered animal tests, two of the beta-blockers were found to cause cancer.