WASHINGTON (AP) _ A consumer group said Thursday that some sunscreens and cosmetics contain an ingredient that can promote cancerous skin tumors and it called on the government to halt their sale.

''Ironically, some sunscreen lotions that consumers apply to prevent skin cancer may increase the likelihood of forming cancerous skin tumors,'' said Mary Ellen Fise, product safety director for the Consumer Federation of America.

The federation said more than a dozen cosmetic products have been sold containing urocanic acid, which it said has the potential in sunlight to promote the growth of tumors by suppressing the immune system.

The federation, joined by two research scientists at The George Washington University Medical Center, petitioned the Food and Drug Administration to ban sales of cosmetics that contain urocanic acid.

''Based on our original research, now supported by other laboratories, it is our scientific opinion that any benefit gained by inclusion of urocanic acid in cosmetics is far outweighed by the potential risks,'' said Dr. Edward DeFabo. The other scientist to join the petition was Dr. Frances Noonan.

The Cosmetic, Toiletry and Fragrance Association said in a statement that urocanic acid is used as a skin conditioning agent at low levels in only a very few cosmetic products.

The trade group said the independent Cosmetic Ingredient Review Expert Panel had asked the cosmetics industry to conduct studies on the safety of urocanic acid but had determined that existing information did not justify a finding it is unsafe, the trade group said.

The trade association said that while studies have indicated urocanic acid can cause immunosuppressive activity in animals, ''preliminary human data indicates there is no cause for concern.''

The non-profit consumer federation said urocanic acid was recently banned for cosmetic use in Australia and products containing it were removed from shelves in Singapore, apparently voluntarily by cosmetic manufacturers.

Fise said that urocanic acid was used to keep the products smooth and well mixed but that most cosmetics use other, safer ingredients to achieve the same result.

''We believe it is important for consumers to discontinue use immediately of sunscreens and skin-care lotions containing urocanic acid,'' she said.

Fise said it may be difficult for consumers to determine whether cosmetics they have already purchased contain urocanic acid as ingredient labels usually appear on outer packaging that may have been discarded.

The consumer group said voluntary reports to FDA by cosmetic manufacturers in 1989 showed that urocanic acid was being used in 15 products, including 10 sunscreens, three body lotions, one makeup base and one makeup foundation.

FDA spokeswoman Bonnie Aikman said the agency is reviewing the group's petition. She said four of the 15 products no longer are on the market.

The products were not identified by the FDA, but the consumer federation said it had recently located in stores eight cosmetic items that contained urocanic acid. They were: Estee Lauder Sun Face Block for Sensitive Skin, Estee Lauder Overnight Pre-Tan Accelerator, Estee Lauder Waterworld Sunscreen, Estee Lauder Oil-Free Tanning Formula, Shiseido Pre-Makeup Cream Base, Shiseido Facial Moisturizing Lotion, Clinique Self-Tanning Formula and Germaine Monteil Pre-Tan.

Rebecca McGreevy, a spokeswoman for Estee Lauder, said the Estee Lauder products were reformulated last September and no longer contain urocanic acid. Clinique spokeswoman Susan Oberstein said the same was true for the Clinique product. James Conroy, a spokesman for Revlon, which owns Germaine Monteil, said the listed product had not been produced for two years and had contained a urocanic acid derivative that was not relevant to the consumer group's concerns. Shiseido said its Pre-Makeup Cream no longer has urocanic acid.

The cosmetics trade group said urocanic acid is listed on the label of any cosmetic product in which it is included.