A scientific committee yesterday warned women, especially those under 25, to shun high-absorbency tampons or use them as little as possible to help prevent the mysterious toxic shock syndrome.

But the committee, a joint panel from the National Academy of Sciences and the Institute of Medicine, said that after two years of study doctors still do not know the cause of the sometimes-fatal disorder. The study was undertaken after a highly publicized outbreak of toxic shock syndrome in 1980.

Enough progress has been made, the group said, to tell women, especially the adolescents and young women most likely to be affected, to minimize use of the kind of tampons usually labeled "super-plus."

By minimize, the group means either avoid these entirely or use them less, committee chairman Dr. Sheldon Wolff of Tufts University said.

"I haven't told my daughter, 22, not to use tampons," he said. "I have told her not to use high-absorbency tampons."

More victims of toxic shock syndrome reported the use of Rely tampons than any other brand, but studies on the possibility of a link between Rely and the syndrome are not conclusive. Rely was withdrawn after the 1980 scare, when the nation counted 867 toxic shock cases in all.

But tampon sales in general are going back up, after a brief decline. Other high-absorbency brands account for 15 to 17 percent of sales and seem to be increasing their share, Institute of Medicine staff members said.

Women who have recently given birth or have had toxic shock syndrome should not use any tampons, the committee added.

The committee said studies since 1980 have produced this information:

* There are probably 4,500 cases nationwide yearly, rather than the 492 officially reported last year. Most do not get reported, or are mistaken for measles or other disorders.

* The cause is still unknown. Eighty-five percent of the victims are stricken during menstruation; and in 98 percent of those cases, tampons were in use, mainly high-absorbency ones.

* But 15 percent of all cases have nothing to do with menstruation and involve both men and women, whites more than blacks. Most of those cases are associated with infections, often following burns or injuries.

* Staphyloccocus bacteria are present or have been present in most cases and seem to produce toxins, or poisons, that cause the shock syndrome.

Beyond these facts, no one knows why the bacteria may cause the disorder in some women and not others. Some scientists think super-absorbent tampons may trap oxygen, spurring bacterial growth. Or these tampons may trap too much fluid, or women may not change them as often, again providing growth medium for bacteria.

But all this is still theory, pending more study, said Dr. Lewis Wannamaker, a University of Minnesota microbiologist.