WASHINGTON — Sen. Olympia Snowe, R-Maine, and 20 Democratic senators asked the Environmental Protection Agency for more information Thursday about an internal paper that reportedly concludes that the gasoline additive MTBE may cause cancer.

Key elements of the document, which has not been made public, surfaced as lawmakers considered whether to shield the makers of MTBE from product liability lawsuits as a result of drinking water contamination in at least 36 states.

MTBE, which was put into gasoline to cut air pollution, has been banned in several states because of complaints that it adds a foul smell and turpentine-like taste to drinking water when it leaks into water supplies. But the draft EPA paper, described as a preliminary document that has not been peer-reviewed, raises broader health concerns about MTBE.

"This is extremely troubling and certainly merits further investigation and review," said the senators in a letter sent Thursday to EPA Administrator Stephen Johnson.

"The possibility that MTBE could have harmful health effects highlights the urgency of implementing an alternative to its use," said Snowe, the only GOP lawmaker to sign the letter.

At high concentrations, MTBE has been found to cause cancer in laboratory mice. As a result, the EPA said years ago the additive could be a human carcinogen, but has not gone beyond that. MTBE is not regulated by the agency.

Meanwhile, intense discussions are underway to try to put together a compromise on MTBE as part of a broad energy bill lawmakers are hoping to complete before the August congressional recess.

A provision that has been pushed by House Majority Leader Tom DeLay and GOP Rep. Joe Barton, chairman of the House-Senate conference negotiating a final energy bill, would protect MTBE makers against product liability lawsuits.

Both DeLay and Barton are from Texas, home of the biggest MTBE makers, including major oil companies.