WASHINGTON -- The government began building the case toward a possible ban of the popular herb ephedra Friday by proposing strong new warning labels that the pills can cause heart attacks and strokes or even kill.

The warning labels -- first proposed in 1997 but blocked until now by the powerful dietary supplement industry -- could be on every bottle by year's end, the first in a series of Food and Drug Administration steps that could limit, if not stop, the herb's use.

But the FDA rankled consumers advocates and some members of Congress by stopping short of an immediate ban of the amphetamine-like stimulant used for weight loss and bodybuilding. The FDA said that despite reports of at least 100 deaths linked to ephedra use, it had not yet compiled enough proof of danger to stand up in court under a 1994 law that severely limits federal safety oversight of dietary supplements.

"This is not the end of the story," promised Health and Human Services Secretary Tommy Thompson, saying a full ban was still possible and the new FDA actions would serve to build the case. "Throughout America, there continue to be tragic incidents that link dietary supplements containing ephedra to serious health problems."

Meanwhile, Thompson advised people, especially athletes or exercise lovers, not to take the herb -- advice that comes two weeks after the latest high-profile death of an ephedra user, Baltimore Orioles pitcher Steve Bechler.

"I would not take this, I would not give it to my family and I don't know why anyone would take these products," Thompson said, pointing to a new review of ephedra by the Rand think tank that found it does nothing to enhance sports performance and causes only temporary loss of a few pounds. "Why take the risk?"

Critics called the Bush administration action a timid step that will cost lives.

Thompson "needs to show the courage to ban this product and be willing to stand up to protect American families," said Sen. Richard Durbin, D-Ill., who said he has counted a half-dozen ephedra-linked deaths just in the six months he has urged Thompson and the FDA to declare the herb an imminent hazard and stop sales.

"Frankly, he should be a lot more afraid of the deaths and injuries from ephedra than of facing attorneys in court," Durbin added.

The American Medical Association praised Friday's action but said more was needed. "The new steps announced today represent real progress toward what we hope will ultimately be a ban on ephedra dietary supplements in the United States," said AMA trustee Ron Davis.

Sen. Orrin Hatch, R-Utah, said, "Today's announcement appears to be a reasonable, if long overdue, step in designing science-based rules pertaining to the use of a product about which public concern has been expressed for many, many years." Hatch was one of the authors of the 1994 law.

The House Energy and Commerce Committee promised congressional hearings on whether a ban was necessary, and the consumer advocacy group Public Citizen said it was considering suing the FDA to force a ban.

Ephedra manufacturers expressed relief that the FDA didn't ban their products, and said they wouldn't fight the new warning labels even though they had lobbied intensely for far weaker ones.

An industry spokesman argued that the Rand study actually proved ephedra works for weight loss and that Thompson's negative interpretation bowed to the critics.

"I respect that Secretary Thompson is under a lot of political pressure and a lot of that has to do with reports in the press and rush to judgment in the Bechler case," said Wes Siegner, general counsel for the Ephedra Education Council.

But also Friday, the FDA warned 24 companies that target their ephedra products to athletes and bodybuilders to stop that misleading marketing within 15 days. There's no scientific evidence that ephedra helps athletic performance, noted FDA Commissioner Mark McClellan.

Ephedra has been linked to life-threatening side effects even when used by healthy people at recommended doses -- because it speeds heart rate and constricts blood vessels. Those effects can be worsened by exercise and use of other stimulants such as caffeine, and they're particularly risky if the user has certain underlying medical conditions such as heart disease, McClellan said.

Canada has long warned consumers not to use ephedra, and the herb is banned in the Olympics. In the United States, it has been banned in professional football, college athletics and, just this week, minor league baseball.

Because ephedra is an herb, U.S. law lets manufacturers sell it over the counter with little oversight to ensure safety. The FDA must prove a clear danger to public health to curb sales. Manufacturers blocked a 1997 FDA attempt to restrict sales of certain doses and put warning labels on the herb by arguing the agency lacked enough proof of danger.

The FDA re-proposed those steps Friday. After a 30-day comment period, the FDA plans within months to put on the front of every ephedra bottle a large warning that death, heart attacks and strokes are possible side effects and that certain people should not use the pills.

Also up for comment are proposed dose restrictions, and whether ephedra poses the kind of risk necessary for a ban.

Ironically, McClellan said, ephedra's active ingredient is a chemical called ephedrine, which when produced synthetically is stringently regulated by the FDA and allowed only in small doses in certain cold drugs.