A Massachusetts state court yesterday ordered a Scituate couple to stop giving their 3-year-old son the highly controversial anit-cancer drug Laetrile, after hearing testimony that the drug was causing chronic cyanide polisoning in the child.

The ruling by Plymouth Superior Court Judge Guy Volterra came one day after the U.S. Supreme Court agreed to review a federal court order intended to allow terminally ill cancer patients to receive the drug, which virtually all elements of the medical establishment have called owrtheless.

Chad Green, the child, has acute lymphocytic leukemia, and was being given chemotherapy at the same tiem he was receiving Laetrile. Without chemotherapy, the disease can kill within four months. With chemotherapy, up to 90 percent of patients being treated survive at least five years, and 50 percent of that group are still disease-free at seven years.

According to Jonathan Brandt, Massachusetts' assistant attorney general, "the boy's body was a laboratory. The facts are that when he was given Laetrile and vitamin A, they caused harm. That's important for the public to know."

According to expert withnesses, the boy had suffered liver damage as a result of the massive doses of vitamin A his parents were giving him in conjunction with the Laetrile. Laetrile advocates believe the drug must be part of an entire therapy, including the consumption of certain "natural" foods and vitamins.

The Green case has been in and out of court for about a year, and Chad's parents said yesterday they will appeal this latest decision.

The case first went to the local probate court when the parents tried to take Chad out of chemotherapy and Massachusetts General Hospital insisted that he continue to be treated. The probate court agreed, and ordered treatment.

The hospital then lost in the state District Court, but won an early round in the Superior Court, where it was ruled that legal custody of Chad be given to the hospital, as in a child abuse cause, but Chad be allowed to live with his parents as long as they cooperated in the treatment. According to Brandt, the question of Laetrile had not been raised up to that point.

The Supreme Judicial Court of Massachusetts affirmed the Superior Court decision, and the matter seemed settled, said Brandt, until Diana Green, Chad's mother, held a press conference last September to announce that Chad had been receiving Laetrile and vitamin therapy.

Brandt said the state then asked that the parents be ordered to submit Chad for regular tests of the levels of vitamin A and thiocyanate -- a cyanide compound -- in his system. The tests, he said, showed a low level of poisoning.

The resulting two-week trial centered on the question of the boy's being given Laetrile.

During the course of the trial a urine test revealed that Chad's thiocyanate level was at least five times what it should have been, "which seemed to show the child was at risk," said Brandt.

Dr. Dean Burk, a retired National Cancer Institute biochemist and perhaps the most respected Laetrile advocate, testified that Chad's thiocyanate level was elevated because of the chemotherapy.

But according to Brandt, Mass General then randomly tested a halfdozen other young leukemia victims on the same chemotherapy and introduced evidence showing that they had thiocyante levels only a fraction of Chad's.