The Environmental Defense Fund filed suit yesterday seeking a ban on the sale of children's sleepwear containing a flame-retarding chemical that is suspected as a cancer-causing agent.

In its lawsuit against the Consumer Product Safety Commission, the fund alleged that the CPSC had not responded rapidly enough to previous administrative petitions seeking to control or end the sale of the sleepwear treated with the chemical.

Recent tests conducted on laboratory animals by the National Cancer Institute show, the EDF has climed, that a high percentage of those animals contracted cancers after eating the chemical, known technically as Tris (2, 3-dobromopropyl) phosphate and called "Tris" for short. It can get absorbed through the skin as well as ingested by an infanct mouthing on a pajama sleeve, the Fund has said.

A year ago, the Fund petitioned the CPSC to place a warning label on fabrics containing Tris. Then, after obtaining the National Cancer Institute data, the Fund sought an outright ban on the sale of such garments.

The CPSC has done nothing to act on those petitions, the Fund charged in its suit, filed in U.S. District Court here. Such inaction, the suit charges, is illegal.

The suit aks further for procedures that would lead to a ban on Tris-treated fabric.

A CPSC spokesman said the commission had no formal reponse, but that it "shares the concern for public health and safety," that it has set April 7 as a date for a decision on the matter and that it believes it has acteed "resonsibly and expeditously."

The use of Tris in garments had dropped markedly in the past year, since the Fund first sought action. A spokesman for the American Apparel Manufacturers Association said recently that no Tris-treated fabrics had been ordered for the upcoming fall season, but hat about 10 per cent of the spring and summer items requiring flame retardants - about 5 million - might contain Tris.