Environmental problems buried in the books of ailing savings and loan institutions could add billions of dollars to the price tag of the thrift cleanup, regulators and environmental lawyers say.

The question of who pays for the cleanup of toxic waste sites inherited by the savings institutions has already pitted one government agency against another and could lead to awkward situations in which the government is forced to sue itself.

At a hearing of the Senate Committee on Banking, Housing and Urban Affairs yesterday, a federal bank regulator differed with a federal environmental regulator about proposed legislation that would limit the Environmental Protection Agency's ability to sue lending institutions to recover the cost of toxic cleanups. Their divergent views prompted the measure's sponsor, Sen. Jake Garn (R-Utah), to say: "There's got to be some sanity out there."

He said EPA should ask Congress for more money if it is needed for toxic waste sites, but it should not "exacerbate" the savings and loan crisis by going after money from insolvent thrifts. Garn scolded James M. Strock, EPA's assistant administrator for enforcement: EPA and thrift regulators are "officials appointed by the same president, so get together."

Even if Garn's proposed measure were passed, environmental problems on thrift properties seized by the government will reduce the chances of recovering losses associated with savings and loan institutions. Properties the government once hoped to sell for substantial sums could be worth much less -- or nothing at all. Some buyers are refusing to bid for properties unless the government promises to pay whatever environmental costs turn up, according to officials of the Resolution Trust Corp., the government agency in charge of disposing of failed thrifts.

More environmental issues will surface as regulators take control of more savings and loan institutions and sift through their portfolios.

So far, the RTC has identified about 300 properties with environmental "concerns" among the portfolios of the S&Ls it has seized.

The Port Liberte project in northern New Jersey is typical of these. When the U.S. government seized control of an insolvent savings and loan institution in New Jersey eight months ago, it hoped to sell the thrift's showcase lending project, a town house and boat slip development nicknamed Venice on the Hudson, for tens of millions of dollars.

Now it looks as though the project could cost the government money because of possible environmental problems. Depending on the outcome of a study now underway, taxpayers might end up paying millions to clean up the site.

In Hawaii, the RTC picked up a seemingly idyllic residential complex when it took control of an insolvent savings and loan association. Called Waiakea Villas and Village, the complex has 202 units, a pool, two tennis courts and landscaped grounds with a fish pond, a lagoon and views of Hilo Bay. But then arsenic was found in the pond and the soil and the 13.6 acre property, which was expected to sell for $7.6 million, remains unsold.

The list of RTC headaches goes on. The portfolio handled by the RTC's Atlanta division -- one of four regional divisions -- includes a leaky underground fuel tank that is contaminating ground water in Florida, buildings with asbestos problems and a commercial building with toxic ground water running across its property. In addition, the Fish and Wildlife Service wants to set aside 15 acres in Florida for wildlife and to protect a wetlands property in North Carolina which has a bald eagle's nest on it.

A recent court case, U.S. v. Fleet Factors Corp., could end up pinning new costs on the RTC. In that case, unrelated to the thrift cleanup, the U.S. Court of Appeals for the Eleventh Circuit widened the definition of laws saying who is responsible for cleaning up toxic wastes.

It ordered creditors who had started overseeing a financially ailing cloth printing company in Georgia to pay $400,000 for the cleanup of 700 drums of toxic chemicals and 44 truckloads of materials containing asbestos.

"The intent of the law ... was to find someone to pay other than the taxpayer," said Jay R. Kraemer, a lawyer in the Washington office of Fried, Frank, Harris, Shriver, & Jacobson. Now that the RTC is a big creditor, "the taxpayer winds up paying anyway," he said.

The RTC isn't the only government agency stuck with this problem. An official of the Federal Deposit Insurance Corp. testified yesterday that the agency has about 270 assets with a total book value of about $365 million with hazardous substance problems. The cost of cleaning up the properties could be three times their market value, said Steven A. Seelig, director of the FDIC's division of liquidation.

"Inability to collect the principal of an asset is one thing," said Seelig. "But findings of ... liability on top of that could jeopardize the financial soundness of a financial institution and the deposit insurance system."

Some environmental advocates fear that the S&L environmental problems could give companies a way to undercut federal environmental cleanup laws. Garn's bill would only hold banks and other lenders responsible if they know about hazardous waste problems and fail to act while in control of the property.

William J. Roberts, legislative director of the Environmental Defense Fund, testified that Garn's bill would discourage lenders from making careful assessments of environmental risks and to discontinue any environmental audits in progress because under the proposed legislation "what you don't know can't hurt you."

Roberts said banks and other lenders would "take a 'see no evil, hear no evil' approach."