Its opposition in the scientific and medical community is impressive and powerful - the American Medical Association, the American Cander Society, the National Cancer Institute and and the Food and Drug Administration have denounced it as worthless.

But that may all be beside the point by now. For the substance know as Laetrile is claimed by its supporters to be a cure for, or least to provide relief from, the tortures of cancer. And dying patients are often far more willing to believe those offering hope than those destroying it.

The dispute over the use of Laetrile is itself a cancer that is metastasizing, or spreading, throughout the FDA and the medical establsihment.

While there have been numerous quack cancer cures, and that is what the American Cancer Society calls Laetrile, none has captured the public imagination or received such widespread patient support as has Laetrile.

At the same time the substance is being called a hoax and a fraud by medical organizations, patients are testifying before state legislature that the apricot extract has saved their lives or made their affliction more bearable.

Indiana, Florida, Texas and Alaska reacted to such testimonials and intensive lobbying from extreme conservative groups by legalization the substance for sale and use in those states, despite an FDA ban - in effect since 1963 - on its interstate shipment.

Had the Laetrile movement come in an earlier era it probably would neither have grown the way it had nor have posed any great threat to the medical establishment. Thirty years ago few patients put the claims of other patients ahead of belief in their physicians and organization such as the AMA.

But Laetrile's popularity has blossomed in an era of ever-increasing awareness of patients rights and the necessity of informed consent. It has come on the medical scene at a time when many patients think of themselves as consumers and are sometimes willing to listen to patient testimonials.

The scientific evidence of Laetrile's effectives is, to be kind, scant.

There have been animal studies of Laetrile at such prestigious institutions as Sloan-Kettering Cancer Institute in Manhattan and Arthur D. Little in Boston, and those studies have shown that Laetrile has no effect in controlling tumor growth in animals.

One several Sloan-Kettering tests evidence of tumor regression, but other scientific, using the same-facilities under the same conditions, were unable to replicate the results. Those original results, therefore are considered to have been a fluke.

Although no one is making serious claims that Laetrile is unsafe - effectiveness - as Dr. Philip Schein, chief of the division of medical oncology at Georgetown University's Lombardi Cancer Center, points out,

"There's no body of data that specific proves Laetrile is safe."

There is, however, strong evidence to suggest that what is being sold as millions of diollars worth of Laetrile is, in fact, not Laetrile.

According to the late Dr. Ernest Krebs Sr., who patended Laetrile, the substance contained cranide, which it released in large quantities only in the presence of an enzyme found in human tumors. It was that release of the poison, he believed, which killed the tumor.

But in an article published a year ago in the British publication New Scientist, a group of researchers reported that they had found what is being distributed as Laetrile and found it to be amygdalin, a product structurally similar to Laetrile but which does not have the same cyanide-releasing properties.

At any rate, for the first time, popular reaction has caused some highly respected scientists and scientific institutions, including the National Cancer Institute, to begin suggesting that the only way to lay the Laetrile controversy to rest is to run human trials of its effectives.

But according to Dr. Alvan Feinstein, professor of eqidemiology and medicine at Yale University, unless a new system is used for classifying cancer patients, such tests would be meaningless.

"The problem is that cancer is defined by its appearance under a microscope," Finstein said.

"It so happens that cancers do grow and spread and do kill, but they do it with different rates os speed. The consequence is that when you find a particular patient with a particular location, it may grow and it may spread but you cannot accurately predict how fast."

Fienstein addsd that "in our present system of classifying cancer, we classify some as inoperable or advanced, and because of the widespread belief that advonced cancer is going to rapidly kill you, if it doesn't it's considered something of a miracle."

"If the patient is being treated with something, it is credited with extending their life, even though they might have lived without it. This applies to orthodox therapy or to something like Laetrile. If they are given Laetrile, the Laetrile is credicted for "extending" the life span."

Feintein an several colegues have, in several prestigious the New England Journal of Medicine, proposed a new system of classifying cancer patients.

Feinstein's theory is that after studying group of patients with similar symptoms and following the progression of their disease, it is possible to catergorize their syptoms and accurately predict the outcome of the other patients with the same symptoms.

"With a properly selected ands properly screened group of patients who were destined to do badly . . . you could try Laetrile out as (as few as) 20 people, and if two of those did well there would be some grounds for continuing the study," he said. "I'm not saying that such a study be done but given the alternative of doing no study or doing a massive, randomized, controlled trail, then what I mentioned would be useful."

Whether such a trial finally proved the efficacy or worthlessness of Laetrile, there is a body of thinking far removed from the controversy that holds that patients, particular terminal patients, should have the right to choose any treatment that will not harm them.

Dr. James Speer, assistant professor of law and medicine at the Institute for the medical Humanities at the university of Texas Medical Branch at Galveston, holds that Americans "have the right of life, liberty and the pursuit of quackery."

"As long as the drug itself is not intrinsically harmful, then the government position is all the more difficult to defend," said Speer."Laetrile does not contribute to alcoholism or drug addition."

The FDA does not see things that way. "We cannot have, within the community, drugs that don't work even if they are promoted only among a small segment (the terminally ill) because they cannot be restricted to that segment," said agency spokesman Wayne Pines.

"It should be illegal [to prescribe Laetrile] and physicians should be prosecuted," said Georgetown's Schein. "Many people out there people out there might well meaning but some are not making money and pushing an inactive therapy on a population that's reaching for a straw."

Schein and other Laetrile opponents say that some people who can demonstrably be helped by conventional, though often highly toxic, yerpapy such as radition and chemothrapy, choose instead to opt for Laetrile and die as a result.

"The claim is being made that it may not be an antitumor agent but it makes people feel better," said Schein, paraphrasing a pro-Laetrile argument that it all right ti give dying patients Laetrile when others in similar situations have been offered morphine and LSD by physicians.

"But I don't see the need for Laetrile" in that context, said Schein.

"We already have (pain relievers) of proven efficacy and safety.

"We don't live by exceptions, we live by precedents, And [if Laetrile use is legalized] there's absolutely no reason why you or I couldn't come up with a new potion, give it to patients, get testimonials from their families and have it distributed."

That may be true, say Laetrila advocated, but, as George Annas, director of the Center for law and Health Sciences at Boston University, says, "if you have a drug that no one willing to say is harmful and people want it certainly terminally ill patients should have a right to have it."

Annas is not, it should be stressed, a Laetrile advocste. Rather, he is one of the nation's leading spokesman for patients' rights and freedom of choice oin medical treatment.

"in terms of Laetrile," he said, "any cancer patient should have a right to get that drug given that they understand what the alternative is. The only good argument against Laetrile that I've heard is that the patient may not take the alternative treatment.

"The patient should understand what the alternative treatment is. As long as you can satisfy yourself that the patient understands the alternatives, the patient should be given what he wants."

"I'm torn on the question," said James Childress, Joseph P. Kennedy Sr. professor of Christian ethics at Georgetown. "My basic starting point or presumption is that people ought to be free to choose whatever therapy they want."

Children said he sees grave difficulties in applying his general principles to the specifics of Laetrile because of the problem that patients may forego life-saving therapy in order to take what they see as the easier route. But he still comes down, he said, on the side of freedom of choice.

"One alternative" to the current problem said Annas, "is to have a massive campaign to educate the public about cancer so they know which ones there are cures for and which there aren't

"The bottom line on Laetrile may be that for some cancers where there is no cure this is the rational choice bacause they are choosing among useless therapies.