A House subcommittee yesterday said it had identified 3,383 chemical disposal sites into which the nation's 53 largest chemical companies have dumped more than 750 million tons of waste -- some of it hazardous -- since 1950.

Some of the sites have long been hidden under parks, churches, homes and farms, the House Commerce subcommittee on oversight and investigations said. The subcommittee said there were 58 sites in Maryland, and 74 in Virginia.

But while the subcommittee passed out a 487-page list of the disposal sites, it declined to tell which ones are dangerous or what any of them contain.

"These sites do not necessarily pose threats to public health or the environment," said Rep. Bob Eckhardt (D-Tex.), who heads the subcommittee. Eckhardt nevertheless said he had asked the Environmental Protection Agency to conduct its own investigation of the sites.

The subcommittee chairman said that if EPA requested specific data about the contents of the chemical dumps the subcommittee would provide it. The subcommittee also recommended in its report that EPA be granted subpoena power in hazardous wastes cases it investigates.

EPA Administrator Douglas M. Costle praised the committee's study yesterday, calling it "a significant step forward in our knowledge of waste disposal sites." An EPA spokesman said that so far the agency has identified 1,469 hazardous waste sites on its own.

Eckhardt said the subcommittee's information was provided by the chemical companies themselves. According to the subcommittee report, 94 percent of the companies' hazardous waste was dumped on their own property. About 400 of those sites have since been closed and sold to other owners, the subcommittee said.

"Many of those closed sites contain w astes with chemical components known to pose potentially serious hazards to the public health andthe environment," the report said. It noted that the sites do not fall under EPA's existing authority to investigate or regulate.

The subcommittee also recommended that a "national inventory" be made by EPA of all hazardous waste sites in the United States and that the agency investigate about 960 waste haulers the House panel said had transported nearly 4.8 million tons of chemical process waste to unknown locations since 1950.

Robert Rowland, president of the Chemical Manufacturers Association, said at the subcommittee's press conference that, while he favored cooperation with the subcommittee and the EPA on waste sites, any cooperation with federal investigators would have to be decided by companies on a case-by-case basis.

Several major U.S. chemical companies are facing multimillion-dollar lawsuits and the possibility of federal and state charges because of their hazardous -waste disposal practices. The subcommittee said its investigation began last year after the discovery of leaks from a chemical dump site at the Love Canal in Niagara FALLS, N.Y., drove residents from their homes.

"Liability is the key point," Rowland said, in any decision by chemical company to reveal the contents of its chemical dump to investigators. He said that the contents of most chemical dumps are known only to a few persons outside the companies that own them.