The Food and Drug Administration has approved commercial marketing for the first time of a drug containing the active ingredient in marijuana, concluding it is safe and effective in treating the severe nausea and vomiting that often accompanies cancer chemotherapy.

Before the drug can be sold commercially, it must jump one more bureaucratic hurdle: the Justice Department's Drug Enforcement Administration.

Scientific studies have shown that a synthetic form of THC, or delta-9-tetrahydrocannabinol, the main mind-altering component in marijuana, can help relieve symptoms in patients for whom other drugs fail.

Following extensive testing in the 1970s, the drug has been available to cancer patients for nearly five years under a carefully-controlled federal distribution system managed by the National Cancer Institute.

FDA approval for commercial marketing was granted to Unimed Inc., a small New Jersey firm.

The government estimated in 1980 that about 200,000 cancer patients undergo chemotherapy each year, with as many as three-fourths needing medication to control resultant nausea and vomiting. At that time, about 50,000 patients were not thought to be helped by conventional drugs, although new anti-nausea drugs have since been marketed.

Paul V. Bollenbacher, president of Unimed, said that more than 20,000 cancer patients have been treated under the free NCI program, which is to end when THC is available commercially. He said the gelatin capsules, which would require a prescription from a DEA-licensed doctor, could be available within 60 days. The cost of the drug, to be sold under the name Marinol, has yet to be determined, he said.

First, though, DEA must reclassify the legal status of synthetic THC capsules under the Controlled Substances Act. Currently, THC and marijuana fall under Schedule 1 with heroin, LSD and other drugs of abuse which have no accepted medical value.

FDA's action makes THC a candidate for Schedule 2, which includes drugs of potential abuse with accepted use in medical treatment.

A spokesman said DEA was awaiting the recommendation from the Department of Health and Human Services and that putting THC in a less restrictive category would take at least two or three months.

"At this point we hope it will be automatic," Bollenbacher said, adding that THC capsules are "undesirable for recreational use. It acts very slowly."

FDA spokesman Edward Nida said he expected little controversy over the approval. "We're talking about a drug intended to be used in severely ill patients who are given a treatment that is a terribly debilitating experience," he said. "We know that some cancer patients have simply made a choice that it isn't worth enduring this to live. The result is going to be we're giving some cancer patients a better shot at staying alive."

Unimed said studies found that only about 7 percent of cancer patients who tried THC stopped because of side effects.