The federal health establishment yesterday took a giant step away from its previous hard-line opposition to Laetrile with an announcement by the National Cancer Insitute that it will conduct an intensive study of the medical records of patients who claim to have been helped by the controversial alleged cancer cure.

Up until now virtually every major component of the health establishment, including NCI, the Food and Drug Administration, the American Cancer Society and the American Medical Association, have called Laetrile worthless, and have argued against further studies of the substance derived from the pits of fruits, particularly apxicots.

Dr. Guy R. Newell, acting director of NCI, event went so far yesterday as to say, "Frankly, it's hard for me to believe that 50,000 to 75,000, Americans are all wrong [about their belief that Laetrile helped them]. That's my personal opinion." Newell added that he didn't believe that large a number of persons could be "duped."

The NCI action comes on the same day that the chairman of the department of oncology [cancer medicine] at the prestigious May Clinic called for a clinical trial of Laetrile on humans.

Writing in yesterday's issue of the New England Journal of Medicine, one of the country's most respected medical publications, Dr. Charles G. Moertel said:

"The Laetrile problem can only be successfully combated if we fight on familiar grounds, using the tools we have known to be most trust- worthy: a tightly controlled clinical trial performed in competent and experienced hands. This approach seems most ethical, and, more important it seems most humane."

Attacking the NCi position, explained in an article by Newell in the same issue of the New England Journal, Moertel argues that "the case-history-review type of study proposed . . . by the NCI seems doomed to failure. No clinical pharmacologist would accept such evidence for the effectiveness of a drug."

Newell, on the other hand, argued both in the journal and at yesterday's press conference at NCI that staging tests on humans before any kind of proff of efficacy has been gathered, would be unethical.

The problem, however, appears to be much more political than ethical. What Moertel has proposed is that trials be staged at several respected institutions, and that only those patients who have tried every other available form of therapy be allowed to participate.

That would not, however, solve the problem of NCI's setting a precedent by circumventing the Food and Drug Administration's requirements that a substance show results in animals prior to testing in humans.

Newell said NCI expects to spend between $80,000 and $100,000 on mailing to physicians and cancer patients, asking that they aid in the study.

Among the information being requested is:

Confirmed pathological diagnosis of cancer (slides must be available for review).

Measurable disease.

Adequate documentation of case history; plus reliably determined estimations of tumor size before and after Laetrile treatments.

Documented interval of therapy with Laetrile as the only anticancer treatment . . . for at least 30 days.

Consent of the patient or surviving next of kin to obtain pertinent office or hospital records as necessary and to publish results.

Newell said yesterday he expects the collection of data, which will begin at the end of next month, to take about three months, and the analysis of the material to take about two more months.

The mailing to physicians will include a letter from FDA Commissioner Donald Kennedy stating that "information gained through the conduct of his study will not be used to identify violations of the Food. Drug and Cosmetic Act . . . No promise of immunity can be offered in reference to illegal activities, but the FDA will not use information obtained through this study to initiate legal action against doctors or patients using Laetrile."

Newall said yesterday that political and social pressure has played a large part in the government's about-face. More than a dozen state legislatures have legalized the use of the substance, and a federal judge has ruled that terminally ill cancer patients may import Laetrile into this country for their personal use.