WASHINGTON (AP) _ An illegally imported powder being sold as an over-the-counter medication for children contains a potentially dangerous prescription drug, the Food and Drug Administration said Thursday.

Agency officials, acting on a tip from New York state officials, found the product, known as ''Comycin Powder for Children,'' at Lee's Oriental Foods in Rochester, N.Y., the FDA said in a statement.

The powder, apparently imported from Thailand, was sold in cellophane packets that bore an English label stating it contained the prescription drug chloramphenicol, which is known to cause fatal anemia in some patients.

Laboratory tests confirmed that the powder contained the prescription drug, the FDA said.

The FDA restricts the use of chloramphenicol for the treatment of meningitis and other severe infections. The drug's label warns against its use to treat colds, flu or other minor diseases because of the potential for severe anemia, the FDA said.

The FDA said the cocoa-flavored powder, which is mixed with water, appeared to be sold for use as a treatment of infections in children.

The powder found at the Rochester market was traced to the Bangkok Market in Brooklyn, N.Y., whose president, Soo Peechaphand, told the agency he had purchased 15 boxes from a Los Angeles wholesaler, the FDA said.

The Bangkok Market is recalling the product from its customers.

The FDA said the Los Angeles company and several other California and New York wholesalers that sell Thai, Vietnamese and Cambodian products denied carrying the product. The agency said it therefore cannot estimate how much was brought into this country.

The manufacturer is listed on the label as Thai Charden Bhaesat.