The controversial drug Laetrile has "now had its day in court" and the scientific evidence has shown, "beyond reasonable doubt," that it "doesn't work" in the treatment of cancer, a leading medical journal said today.

"The time has come to close the books on Laetrile," contended Dr. Arnold S. Relman, editor of the New England Journal of Medicine. He said that research had confirmed what many in the medical community had earlier suspected: "Laetrile can be considered neither effective nor safe."

His condemnation of the controversial drug, which has been widely used as an underground cancer treatment, is based on the negative results of a large-scale federal study published in this week's journal.

Researchers at prominent institutions concluded Laetrile is a "toxic drug that is not effective as a cancer treatment." They studied effects of the apricot-pit derivative in 178 advanced cancer patients.

Although the overall results were publicized at a scientific meeting last spring, the published findings emphasize the possible toxicity of Laetrile and warn patients about the "danger of cyanide poisoning" which could be lethal.

In a strongly worded editorial, Relman said, "no sensible person will want to advocate its further use and no state legislature should sanction it any longer."

Dr. Charles Moertel of the Mayo Clinic, who headed the study, also warned that the toxicity of oral preparations of Laetrile documented in the study, as well as the contamination of products received from manufacturers in Mexico, "must be considered by persons in state legislatures and the federal courts who are charged with protecting the public safety."

He said anyone still receiving Laetrile should be carefully monitored for increased levels of cyanide in the blood, a precaution, he said, Laetrile therapists have not commonly used.

Moertel noted that Laetrile "completely eclipsed any other unorthodox therapy ever used for any disease in our time" and that it has been legalized in 27 states. It is "also legal for use nationwide under a federal court order, which, although it has been reviewed by the United States Supreme Court, has not been reversed."