he Food and Drug Administration moved yesterday to impose new rules on dietary supplements that would force manufacturers to make clean and accurately labeled products.

The changes will not tell consumers whether the supplements — like vitamin C, ephedra, St. John's wort and ginkgo biloba — are dangerous nor whether they work.

The agency, officials said, is responding to many cases in which bacteria, glass, pesticides, lead and other contaminants have been found in food supplements, and to cases in which products had more — or, more commonly, far less — active ingredient in each pill or capsule than the label claimed.

"This has been a `buyer beware' market," Dr. Mark B. McClellan, the F.D.A. commissioner, said in the announcement, in which he estimated that 1,000 domestic and foreign companies make supplements sold here. "Millions of Americans use dietary supplements every day, and we need to make sure they're getting the products they pay for."

Consumer groups and critics of the industry applauded the move, but said it was long overdue and still inadequate. The F.D.A., they said, has for nine years had the power to impose good manufacturing standards, but has not done so.

They said it was only the first step toward protecting users of supplements, which are derived "naturally" from leaves, roots, rocks and animal parts but can be just as pharmacologically powerful and dangerous as the drugs the agency does regulate.

"Good manufacturing practices are a step in the right direction, but they're not going to solve most of the problems out there," said Tod Cooperman, the president of Consumer- Lab.com, a White Plains laboratory whose work uncovering contaminants in supplements was cited yesterday by the F.D.A. "Now the critical issue is enforcement."

The agency's efforts to regulate "natural remedies" were hobbled by the 1994 Dietary Supplement Health and Education Act, which defined them as dietary supplements and put them in a category somewhere between food and drugs. While pharmaceutical manufacturers must spend millions to prove to the F.D.A. that their drugs are safe before they are marketed, the burden of proving that a supplement already on the shelves is hazardous rests with the agency.

Under the 1994 law, the agency had the power to enforce manufacturing standards, but until yesterday's announcement, it never issued specific regulations on what companies had to do to comply or indicated that it would enforce those rules.

Several large supplement makers and industry groups welcomed the announcement, saying that they already had voluntary manufacturing and purity standards and that F.D.A. regulation would flush out shoddy companies that ruin the market.

"We agree with what the F.D.A. has done," said David Seckman, executive director of the National Nutritional Foods Association. "Once the regulations are final, they will strengthen consumer confidence."

Robin Gellman, a spokeswoman for the American Herbal Products Association, said she was "sorry it took so long."

"But," Ms. Gellman added, "it's irresponsible for the F.D.A. to insinuate that supplements aren't regulated. It's not like it's the Wild West out there and this is Day 1 of regulations. It's illegal to have a product with an adulterant in it, and they have pulled products off the market."

Consumer activists said that in the absence of strict F.D.A. enforcement the industry had largely policed itself and decided whether to disclose voluntarily bad reactions to its nostrums.

Bill Gurley, a University of Arkansas pharmacologist who has studied products containing ephedra, the weight-loss product suspected in last month's death of Steve Bechler, a Baltimore Orioles pitcher, called the current situation a "madhouse." In a study three years ago, Mr. Gurley found that half the brand-name ephedra products differed from label strengths by at least 20 percent. Some had other drugs that should have been on the label, and some had heavy metals.

In its announcement, the F.D.A. cited several cases of mislabeled or contaminated drugs, including these:

¶An unnamed company recalled its products after finding lead in them.

¶Another company recalled a niacin product after reports of heart attacks, vomiting and liver damage. One of its suppliers apparently mislabeled a bulk container that had held 10 times the safe amount of niacin.

¶Five of 18 soy or red clover products tested by a private laboratory had as little as half the amounts of isoflavones they claimed.

With its announcement yesterday, the F.D.A. published 547 pages of proposed regulations. They include rules for designing and building plants, for controlling quality, testing ingredients, keeping detailed records and handling consumer complaints about harm done by the products.

After reading the rules, Mr. Cooperman said, he saw nothing about factory inspections or random testing. If the rules are not enforced, he said, "we may not end up much better off than with what we've got already."

Dr. McClellan said there would be a 90-day comment period on the proposed rules. He said he hoped to be enforcing them on large companies by next year, though some might voluntarily comply earlier. Small companies would get a three-year grace period.

Dr. Sidney M. Wolfe, director of the Public Citizen Health Research Group, said he believed that the safe-manufacturing practices were welcome. "But," Dr. Wolfe added, "that begs the enormously larger issue. There's no requirement to show that it's safe or effective. Yes, you will now be getting 20 milligrams of what the label says should be 20 milligrams, but there's no more or less guarantee as to whether you'll be killed or injured or defrauded because it doesn't work."