BANGKOK, Thailand (AP) _ Hundreds of radiation-treated gems are circulating in Asia and possibly Europe, endangering jewel dealers, cutters and owners, a leading gem expert warned today.

The stones _ all of them a kind of stone known as cat's eyes _ apparently were bombarded with radiation to change their color from yellow to the much more sought-after brown, said Ken Scarratt, president of the Bangkok Center for Gemstone Testing.

``When we first tested one with a Geiger counter, it pushed the needle off the dial,'' Scarratt said.

His center, Thailand's premier gem lab, has alerted Thai officials, jewelry trade associations and dealers around the world over fears the irradiated stones could cause skin cancer.

Authorities in Hong Kong and Indonesia already have reported finding some of the radioactive gems, and Scarratt said the stones are also believed to be circulating in Japan.

The stones emit 26 times the level of radiation accepted as safe in Asia and 52 times the acceptable level in the United States, according to tests at the Thai government's Office of Atomic Energy for Peace.

Scarratt said he believed the stones came from Indonesia, where they were bombarded with radiation in a nuclear reactor.

``The gems they start with are not usually the highest quality, but by irradiating them to change their color, the dealer can get five or 10 times the price he would have gotten for them in their normal state,'' said Tom Banker, managing director of GemEssence, a jewelry company in Bangkok.

Banker said top quality chocolate-colored cat's eyes can get as much as $1,000 a carat wholesale, and twice that retail.

``They're much rarer than diamonds or rubies,'' Scarratt said.

Experts fear the irradiated stones could cause skin cancer or other kinds of cancer. They could be especially dangerous to any gem finishers who unknowingly cut into one to improve the shape _ since they might inhale radioactive dust.

Consumers should avoid buying dark brown cat's eyes, or if they can't resist, have the stone tested first, Scarratt said.

Scarratt said he didn't expect the scare would hurt the Thai gem and jewelry industry, whose wares are one the country's top 10 exports, since only one type of stone was involved.

Thailand has emerged as a high-quality finishing center for diamonds and rubies and sapphires mined in Thailand and neighboring Cambodia and Burma.