Two scientists warned yesterday that the children's sleepwear banned by the government because it might cause cancer also might cause abnormalities in the reproductive systems of boys.

The scientists said that the sleepwear was treated with a flame retardant, Tris (tris-BP), which is chemically closely related to a pesticide, DRCP, which has been linked to sterility in workers who make it.

In addition, said biochemists Arlene Blum and Bruce N. Ames of the University of California at Berkeley, DBCP - in trace amounts - is present as an impurity in tris-BP.

Blum and Ames discovered nearly two years ago that tris-BP was a mutagen, an agent capable of causing changes in genetic material, and at that time recommended that it be kept out of children's sleepwear.

Since then, they recalled in a letter to Chairman S. John Byinton to the Consumer Product Safety Commission, tris-BP has been shown to be a potent cancer-causing agent in animals, to be absorbed from fabric by human skin, and to atrophy the testicles of rats and rabbits.

In April, after studies confirmed the cancer hazard of tris-BP, the commission banned the manufacture and sale of sleepwear treated with it. But legal challenges and other problems have partially frustrated the ban, forcing the agency to go to court on an individual basis against distributors and retailers that continue to sell treated garments.

Blum and Ames told Byinton of "new information that reinforces our fears" that boys who have worn pajamas treated with tris-BP may suffer sterility, sperm mutations and testicular abnormalities.

Like tris-BP, they wrote, DBCP (bibromochloropropane) is a mutagen and a carcinogen, atrophies animal testicles, and recently has been shown to cause human sterility.

At least 60 male chemical workers have been found to be sterile at a Dow Chemical Co. plant in Magnolia, Ark., and at an Occidential Chemical Co. plant in Lathrop, Calif., which uses Dow products. Tests are being made on scores of additional DBCP workers at Dow plants in Midland, Mich., and Shell Chemical Co. plants in Denver.

Last Thursday, Dow recalled all outstanding stocks of the pesticide. BOth Dow and Shell had reported in 1961 that DBCP caused sterility in animals, but the government never tried to protect workers from possible sterility.

In a letter to Byinton, Blum and Ames said that "DBCP has been shown to cause sterility in humans at doeses of tris-BP which children can absorb from their sleepwear."

Moreover, they said, "The risk of reproductive effects on children from Tris-treatment pajamas is amplified because the scrotum is about 20 times more permeable to chemicals than in other skin."

They warned that absorption "of even small doses of tris-BP could cause cancer and reproductive abnormalities in this generation and birth defects in future generations."

Yesterday, Byington said the commission will consider recommendations made by Blum and Ames, including a registry to track thousands of children exposed to flame retardants and compare them with unexposed children.

He told a reporter that the agency has enlisted the National Institute of Occupational Safety and Health to help evaluate possible hazards of tris-BP to reproductive systems. But "the regulatory process is over," he said. "We are doing what we can . . . to get treated garments off the market."

Commission member R. David Pittle said, "We must redouble our efforts to be sure that treated garments are not on the shelves." The Environmental Defense Fund, the nonprofit group whose initiative led to the ban, now wantst the agency to require disclosure labels on all treated garments offered for sale.

Blum and Ames said that, to meet federal requirements that children's sleepwear be flame-retardant, some producers now treat them with tris-CP, in which chlorine replaces the bromine in tris-BP.

"We have now shown that tris-CP is a mutagen," they said. They did so with tests in which nearly all substances found to be mutagenic also are carcinogenic. With both forms of tris in garments being sold everywhere, they said, "Children are being exposed to large doses of the chemicals, both through direct absorption from fabric and from chewing on their sleepwear."