As part of a crackdown on false and deceptive diet claims, the Federal Trade Commission sent letters to nine media companies yesterday, reminding them to stop publishing ads for bogus weight-loss products.

The letters went to publications that ran ads for products that were the target of six lawsuits filed by the agency within the past week -- pills, powders, green tea, topical gels and patches that promised significant weight loss, even if consumers didn't decrease their food intake or increase their exercise.

The agency is seeking a halt to the ads and consumer refunds for such products as the "Himalayan Diet Breakthrough" -- a dietary supplement of what the manufacturer called Nepalese Mineral Pitch, a paste-like material that "oozes out of the cliff face cracks in the summer season." The product, which costs $39.95 for a month's supply, promised consumers could lose as much as 37 pounds in eight weeks if taken before lunch, dinner and bedtime.

With Chinese Diet Tea, dieters were told they could lose as much as six pounds a week if they drank a cup after each meal to neutralize the absorption of fattening foods. It costs $24.95 for a 30-day supply.

"These claims are about as credible as a note from the tooth fairy," said agency chairman Deborah Platt Majoras. "But they ran in the pages of well-known national magazines and big city newspapers and on popular Internet sites, all of which lend an air of credibility to these outlandish claims."

Majoras, who became head of the FTC in August, has said she wants the agency to play a more active role in the national campaign against obesity.

Majoras said the agency has seen the number of deceptive ads cut by half since December, when the FTC sent a guide to media outlets to help them spot and refuse ads making bogus claims.

Yesterday's letters went to Cosmopolitan, Woman's Own, Complete Woman, USA Weekend, Dallas Morning News, San Francisco Chronicle, Cleveland Plain Dealer, Albuquerque Journal and the Spanish-language magazine TeleRevista.

It was the first time the agency sent letters to publishers in conjunction with lawsuits against diet-product makers. The FTC estimates that Americans spend $37.1 billion a year on weight-loss products and said media firms have benefited substantially with their promotions.

"We know that no publication or station wants to knowingly print or air false weight-loss claims or mislead its audience," the letter to the publications said.

Majoras said the agency was not planning any legal action against any media company for running the ads.

Because the letters were just sent, the recipients had not yet received them, and most declined to comment yesterday.

Brian Fantl, general manager of the Albuquerque Publishing Co., said he thought the Journal published one ad, for the Himalayan Diet Breakthrough, almost a year ago and only once. "We haven't heard a complaint since." Newspapers, he added, "get thousands of ads a year, and I don't know anyone in the position to verify every item and every claim of every ad."

Howard Polskin, a spokesman for the Magazine Publishers of America, said: "We strongly support the principle of truth in advertising and continue to believe the best way to achieve these goals is in taking vigorous enforcement actions and not by making publishers responsible for advertising claims."