A drug that could help as many as a million Americans with epilepsy will be approved by the Food and Drug Administration next week, after what many doctors have regarded as months or years of unjustified delay.

The drug is sodium valproate, which has been used in Europe for 10 years on more than 200,000 patients with wide success.

Documents approvingits use in a wide variety of epileptic and related seizures are being prepared by FDA officials FDA sources said yesterday.

"This is delightful news," said Dr. Eli Goldensohn, professor of neurology at Columbia University in New York and chairman of a panel of specialists who this month urged FDA to give the drug immediate approval.

"There are 2 million epileptics in the United States" Goldensohn said, "and about a million are not well controlled by present drugs. I would say that within a very short time sodium valproate will take its place alongside the major compounds we now use to control seizures."

The panel Goldensohn headed - one assembled by the Epilepsy Foundation of America - was the third in the past year to urge FDA to approve valproate. The others were a congressionally created National Commission for the Control of Epilepsy and the FDA's Advisdry Committee on Neurologic Drugs.

The FDA overruled its advisers' recommendation, saying it had not yet been shown enough evidence that the drug had been effective in at least two well-controlled trials with epileptic patients.

In reply, the Goldensohn panel said there are more than 200 favorable reports in world medical literature, with "at least" 30 of them well-conducted clinical trials on a total of more than 1,300 patients.

FDA officials have decided that at least two of the trials provide evidence that valproate works and is usually safe.

But both FDA officials and FDA's critics on this issue have said that the basic obstacle to the drug's use in this country was the failure of any American firm to seek FDA approval until 1974.

Abbott Laboratories of North Chicago, III., then became the only one of 10 U.S. firms to say yes when the drug's French manufacturer tried to mind an American licensee. As the drug market goes, observers say, even a million patients may not create a profitable enough market for a major firm to bother with.

Many federal officials and health experts have been discussing the need for some mechanism - perhaps federal contracts - to encourage drug-makers to develop drugs that vitally needed but lack mass markets.

Until now, valproate's only use in this country has been in experimental trials and in other small groups under special FDA permission.

The FDA, it was learned, will approve the drug's use as either sole therapy or adjunctive therapy (treatment in combination with other drugs) for absence and petit mal seizures - seizures characterized by brief loss of consciousness - and as adjunctive therapy for "multiple seizure types, including petit malu a phrase that Goldensohn said "takes in just about everything else."

One FDA official said Abbott and FDA would shortly agree on official labeling for the drug, and expanded supplies might start reaching the market by April.