The Supreme Court ruled 9 to 0 yesterday that the federal drug law allows no exception from its safety and effectiveness requirements for Laetrile, a controversial purported cure for persons believed to be dying of cancer.

The ruling opens the way for the U.S. Food and Drug Administration to reimpose its previous ban on interstate shipment of Laetrile because it has not been shown to be safe and effective under the Food, Drug and Cosmetic Act.

Seventeen states, including Maryland, have leagalized the prescription and use of Laetrile within their borders. But the state laws have not done much to circumvent a ban on interstate shipments of Laetrile, according to an FDA spokesman.

An estimated 50,000 to 75,000 American cans have taken Laetrile. Many have gotten it in Mexico. Some - as a result of smuggling schemes - have gotten it in the United States. Several persons involved in the schemes have been convicted. The court has refused to disturb the convictions.

The name Laetrile is applied mainly to a substance usually derived from apricot pits, but also has been used for chemical compounds similar to, or consisting at least in part of, amygdalin, a chemical present in the kernels or seeds of most fruits.

The National Cancer Institute announced in January 1978 that it was launching an intense study of patients claiming to have been helped by Laetrile. The substance repeatedly has been denounced as useless by leaders of the FDA and the American Medical Association.

Justice Thurgood Marshall wrote the opinion for the court, which overturned pro-Laetrile decisions by U.S. District Court Judge Luther L. Bohannon of Oklahoma City and by the 10th U.S. Circuit Court of Appeals.

Initially, Bohannon ordered the FDA to hold an administrative hearing. The agency complied and concluded that Laetrille - or products using the name - was a "new drug" under the law, and thus had to be proven safe and effective. The FDA said that neither experts nor acceptable scientific studies could prove Laetrile safe or effective. Bohannon rejected the FDA findings and ruled that Laetrile could be prescribed.

During Supreme Court oral argument, Marshall asked the lawyer for persons seeking to legitimize Laetrile if Bohannon had not simple thrown out the FDA's findings "and substituted his own?" The lawyer replied, "That's exactly what he did."

The appellate court did not go along with Bohannon. But, in an opinion by Chief Judge Oliver Seth of Santa Fe. N.M., it permitted physicians nationwide to administer Laetrile intravenously to patients "certified" to be terminally ill.

The substance has been found by the FDA to be toxic in some patients when taken by mouth. Tests to show it to be either toxic or nontoxic when injected have not been done.

In permitting intravenous use of Laetrile, the appeals court found that "that 'safety' and 'effectiveness' terms used in the statute have no reasonable application to terminally ill cancer patients."

As a result, Seth concluded, there were no realistic standards against which to measure the safety and effectiveness of any drug for such persons.

The government's rejection of both the Bohannon and the Seth rulings was echoed by Marshall with an opinion warning that to deny the FDA's authority over Laetrile for the terminally ill would be to deny its authority "over all drugs, however toxic or ineffectual, for such individuals."

The drug law "makes no special provision for drugs used to treat terminally ill patients," he wrote. "Nothing" in its history "suggest that Congress intended protection only for persons suffering from curable diseases. To the contrary," he said, "Congress expressed concern that individuals with fatal illnesses, such as cancer, should be shielded from fraudulent cures."

Rejecting the 10th Circuit's conclusion that the law cannot resonably apply to the dying, Marshall said the appellate court had confused effectiveness with a capacity to cure "In the treatment of any illness, terminal or otherwise, a drug is effective if it fulfills, by objective indices, its sponsor's claims of prolonged life, improved physical condition or reduced pain," Marshall said. Similarly, he said, "a drug is unsafe if its potential for inflicting death or physical injury is not offset by the possibility of therapeutic benefit."

Maryland, cancer patients have been able to obtain Laetrile by filing affidavits of need, which are then used to obtain the drug from Mexico. That system has a court's sanction, but the FDA now plans to ask a federal appeals court to disallow it in light of yesterday's Supreme Court decision, according to an FDA official.