Psychiatric researchers have found a drug now in common use for a number of ailments also can improve memory greatly, according to a report yesterday in the journal Science.

In tests on a small number of subjects, the drug has been found not only to improve the memory of normal people by 20 percent in two types of tests, but also to have an even more powerful effect on patients with disabling depression. And it induced a stunning 300 percent improvement in the recall of patients who have just undergone electroshock, a therapy that commonly results in amnesia.

The drug, Vasopressin, prescribed to constrict blood vessels or help the kidneys retain water, was given to improve memory in a battery of three tests on 18 people studied by Drs. Herbert Weingartner, Frederick Goodwin, Philip Gold and others at the National Institutes of Mental Health.

Yesterday's report was the first to document the memory-enhancing effects of Vasopressin in humans, although several animal studies had showed similar results. Goodwin also said a Dutch researcher, Dr. DeWied Legrof, has demonstrated similar powerful memory effects in some 40 people, all over 50 years old. Legrof's patients showed "a big improvement in memory; for some of them it was like getting back the memory they had as much younger people apparently," Goodwin said.

Since Vasopressin has dangerous effects on the body's circulation and water retention, it cannot be sold as a memory drug in its present form. But a chemically similar version of the drug has been made that reduces these effects and appears in animal tests to retain memory effects. But this version is many years from being sold on the open market because of the extensive testing required, according to a spokesman for Organon, the Dutch pharmaceutical firm that has done the most work on it.

In the Science report, 12 of the 18 subjects were college students, and they were first given memory tests, then given Vasopression or a placebo (an inactive substance) in a nasal spray. The drug was given several times a day for two to three weeks.

The students were read 11 unrelated words, then were asked to repeat them, in order, from memory. The students improved their performance by an average of 20 percent when given the drug. In another test, the words were all in a single category, such as items of furniture, and after some time, the students were asked to recall them. The performance again increased somewhat more than 20 percent.

The researchers also tested four patients afflicted with depressions. Their before-test memory scores were lower than average for persons of their age. After being given Vasopressin, they improved 50 percent on words in one category, and increased almost 100 percent on a third word-recall test.

The most dramatic increases came when Vasopressin was given three patients about to undergo electroshock therapy. All three improved their recall of words by 300 percent, with a higher-than-usual statistical reliability Goodwin said.

Goodwin also said he is aware of some uncontrolled studies in which amnesia has been dramatically reversed while patients take the drug.When the drug is removed, however, the amnesiacs apparently relapse.

The effect of the drug in all the tests continued for about three weeks after the treatments stopped, Goodwin said.

While the new version of Vasopressin cannot be put into general use, it can be used experimentally to a degree. Goodwin said it would likely be used in cases of amnesia and in selected cases of psychosis, and other clinically experimental uses. But the medical precautions and monitoring required will make it a cumbersome treatment.