The Food & Drug Administration plans to require warning labels on all brands of tampons informing women of an apparent link between tampon use and toxic shock syndrome, the mysterious illness that has struck more than 300 young women.

One tampon product, Rely, was taken off the market Monday by its manufacturer, Procter & Gamble Co., after a government study showed a high percentage of victims of toxic shock syndrome had used that brand.

Such a close link has not been established between the illness and other brands, but an FDA spokesman said yesterday that women may want to reconsider the use of any tampon products until the cause of the illness is better understood.

"While the recent study's results clearly indicate that women should stop using Rely tampons, women that wish to reduce their risk of toxic shock syndrome even further may want to consider not using any tampons, or using napkins rather than tampons part of the time during their menstrual periods," an FDA spokesman said.

The FDA will be meetiing with major tampon manufacturers in the next few days to review the evidence about the risks of variouos tampon products. "If a company can make a case that its brand does not need a warning label, we'll listen," the spokesman said.

The agency also will ask the manufacturers to join in a public educational campaign to alert women and the medical profession of the symptoms of the disease.

The FDA is not considering a total ban on tampon products at this point, a spokesman said.

Toxic shock syyndrome is a newly recognized bacterial infection that causes a sudden drop in blood pressure, accompanied by high fever, vomiting, diarrhea, and in some cases, severe shock. Since January, 344 cases have been reported, 300 of them in women. Since 1975, at least 25 deaths have been blamed on the disease.

Dr. Bruce Dan of the Center for Disease Control in Atlanta said yesterday that researchers still are searching for the link between tampon use and toxic shock syndrome.

So far, they have found nothing in the tampons that could explain the connection, he said, although research continues in several directions: One theory is that the tampon provides a breeding place for the toxic bacterium; another is that the plastic device used to insert the tampon may cause abrasions in the vagina that permit infectious bacteria to enter the blood stream. "The manufacturers are just as puzzled as we are," he said.

A spokesman for Tampax, the leading tampon producer, said the company would wait until after it meets with the FDA before deciding whether it thinks a warning label is necessary. It will support a public educational campaign, the spokesman said.

Spokesmen for Johnson & Johnson and Esmark, which manufacturers the Playtex tampon, said their companies also will support a public educational program.

CDC researchers believe the source of the syndrome is a bacterium, staphlococcus aures, with a strong resistance to common antibiotics. The CDC studies indicate that this bacterium is present on the bodies of a relatively few women.

Among the victims, however, the bacterium apparently produces a toxin (poison), which causes the shock syndrome illness after entering the bloodstream.

Although the risk would appear to be low, striking only three out of every 100,000 women of menstruatinng age, Dr. Dan cautioned that if the strain of bacterium is new, as he believes, the full dimensions of the problem cannot yet be known.

A new death attributed to toxic shock syndrome was reported Tuesday. Dr. Richard Fransworth, chief pediatric resident at Tucson Medical Center, said it was "almost certain" that the disease killed a 16-year-old high school student, Michelle Rossell, who died a week ago.