Computer users surfing the Internet to look for a remedy for painful joints can type in the words "arthritis cure" and get a list of more than 10,000 Web sites, many of them promising miracles. But if they go to the home page for a product called ArthritiCure, they're in for a surprise.

"Be pain-free FOREVER!" "Read our testimonials!" "Only $19.95!" declares the advertisement. But if you click anywhere on the ArthritiCure home page, the next message you read warns, "You could have been SCAMMED!" and offers advice on how to recognize fraudulent health claims.

ArthritiCure doesn't exist. The Web site, brought to you by the Federal Trade Commission (FTC), is part of a new effort by that agency to crack down on fraudulent advertising for health products on the Internet. By going after some of the worst offenders and by educating consumers, the FTC is trying to cope with a flood of phony treatments and cures being peddled online.

"The Internet has become a very yeasty place for fraudulent operators . . . to pursue old-time scams," said Jodie Bernstein, director of the FTC's Bureau of Consumer Protection, at a news conference last week announcing Operation Cure.All, the new project.

Last year more than 22 million Americans used their computers to seek medical information, making health concerns the sixth most common reason for using the Internet. The number of people going online for this purpose is growing by 70 percent a year, said Scott Reents, of the market research firm Cyber Dialogue Inc., who noted that women and seniors make up an increasing share of such Web surfers.

Much of what they can find online is reliable and helpful: sites operated by government agencies, medical schools and teaching hospitals, consumer organizations, support groups and reputable doctors. But they'll also encounter quacks galore. "Sites touting remedies for serious diseases like cancer, heart disease, HIV/AIDS and arthritis are exploding," Bernstein said.

A team of Web surfers at the FTC visited about 800 sites--400 in 1997 and 400 in 1998--that contained questionable claims for products purporting to treat or cure six serious diseases. In each case, the agency sent an e-mail message to the owners advising them that such claims must be scientifically substantiated and that they might be violating federal law.

When FTC employees revisited a sample of the 1998 sites two months later, they found that in 28 percent of the cases, either the site or the questionable claims were gone. In 10 percent of the cases, some change had been made. But at the majority--62 percent--there had been no change in content.

Last week, the agency announced that it had charged four companies with making unsubstantiated health claims for products advertised on the Internet. In each case, the company agreed to settle and is prohibited from making such claims for products in the future. Under the terms of the settlements, those charged must make periodic compliance reports to the FTC and must show the agency their advertisements, said Richard Cleland, a staff attorney who directs Project Cure.All.

One company, Arthritis Pain Care Center, marketed CMO, a fatty acid obtained from beef tallow, as an arthritis cure. Another, Body Systems Technology Inc. (BST), sold shark cartilage capsules and products containing cat's claw, a Peruvian plant, promoting them as treatments for cancer, AIDS and arthritis. BST was ordered to notify purchasers and refund their money.

Two other companies, Magnetic Therapeutic Technologies Inc. and Pain Stops Here! Inc., promoted magnetic therapy devices to treat such ailments as cancer, high blood pressure, liver disease and arthritis.

The U.S. Food and Drug Administration (FDA) can also take action against Internet site operators if claims made for medical products violate labeling laws, said Gary Dykstra, deputy associate FDA commissioner for regulatory affairs. "The FDA, just like the FTC, has got to look at these things on a case-by-case basis," he said.

There are thousands of sites promoting health products on the Internet, far too many for the federal government to police effectively, the FTC's Bernstein acknowledged.

"They're like mushrooms," said David Schardt, an associate nutritionist at the Center for Science in the Public Interest, a consumer organization. "You can cut them down or trim them back and they keep reappearing. . . . By the time the FTC has contacted 400 of them, there are 400-plus more sites. It just grows exponentially."

Since 1994, the FTC has brought charges for fraudulent advertising against the operators of 91 Internet sites, including eight that sold health-related products. Bernstein said the agency hopes such actions will deter other would-be snake oil peddlers.

The FTC advises consumers to beware of marketing, on the Internet or elsewhere, that uses the following techniques:

* Claiming the product will quickly cure a variety of ailments.

* Using words such as "scientific breakthrough," "secret ingredient" or "ancient remedy."

* Using impressive-sounding "medicalese."

* Claiming the government, scientists or the medical profession have conspired to suppress the product.

* Including undocumented case histories or testimonials citing miraculous results.

* Advertising the product as available from only one source.

The ArthritiCure home page is part of an FTC effort to reach and warn consumers who may be vulnerable to fraudulent health claims. The agency has created similar Web pages advertising two other nonexistent products, a purported weight loss aid called NordiCaLite and Virility Plus, which claims to be an alternative to the impotence treatment Viagra.

Computer specialist Dawne Holz, who designs FTC Web sites for consumer and business education, said the agency has put 12 such "teaser sites" on the World Wide Web to educate people about questionable marketing tactics. "We advertise them to search engines or we wait for the search engines to send their spiders out" and find the sites, she said.

To check out products that sound too good to be true, FTC officials suggest asking a doctor, pharmacist or--what else?--going on the Internet. A major government site at www.healthfinder.gov provides links to 5,000 reliable health resources. The FTC's home page, with advice on how to evaluate diet, health and fitness products, can be found at www.ftc.gov.

CAPTION: Visitors to the main Web page for NordiCaLite, one of 12 "teaser sites" created by the FTC, quickly reach a page warning them to tread carefully on the Internet.