Given their best chance in years of persuading Congress to overhaul the nation's pesticide regulations, environmentalists are sharply divided over ways to exploit the opportunity.

The split among environmentalists threatens prospects for revising the outdated Federal Insecticide, Fungicide and Rodenticide Act (FIFRA), according to congressional sources. Chances for such legislation are considered good this year because of the new Democratic control of the Senate and a recent National Academy of Sciences report spotlighting lapses in existing law.

At issue is whether environmentalists should fight for strong FIFRA legislation in both houses or concentrate their resources on the Senate, in the hope that a strong bill passed there would eventually be approved in a House-Senate conference dominated by pro-environmental House members.

The controversy erupted after House Energy and Commerce Committee leaders tried to get the strategy moving. In a deal proposed to the Agriculture Committee, which has primary jurisdiction over FIFRA legislation, they offered to support a House bill approved last October that Agriculture Chairman E (Kika) de la Garza (D-Tex.) has said he wants to pass again.

Sources said Energy and Commerce Chairman John D. Dingell (D-Mich.) and health and environment subcommittee Chairman Henry A. Waxman (D-Calif.) conditionally pledged not to try to amend the October bill, which contains major provisions opposed by environmentalists.

In exchange, they asked de la Garza for assurances that they would be chosen as sole negotiators for the House on some of those provisions if the Senate passes a different FIFRA bill and a conference is empaneled.

Environmentalists said the strategy is to pass a FIFRA bill quickly, send it to the Senate to be strengthened and wait for a conference where Energy and Commerce members can better shape environmental issues. Sen. Patrick J. Leahy (D-Vt.), an avid supporter of environmental protection, is chairman of the Agriculture Committee, having succeeded conservative Sen. Jesse A. Helms (R-N.C.).

"We'd like to see the bill strengthened," Waxman said. "I'm hopeful we can improve it in conference."

A spokesman for de la Garza said the chairman thinks the two sides "are close to agreement."

The strategy is strongly opposed by several environmental groups, which are not as optimistic about a strong Senate bill and are not willing to acquiesce as the House again passes legislation that they consider worse than existing law.

The measure would prevent states from adopting pesticide limits on food products stricter than the federal government's if it found that its standards were sufficiently protective. It would also exempt agricultural producers from liability to clean up environmental damage caused by pesticide spills.

Rick Hind, environmental lobbyist for the Public Interest Research Group, said that Dingell and Waxman would be "paying a high price and taking a great risk" by supporting the October bill because they have no certainty of deleting objectionable provisions in a conference.

He said that if de la Garza succeeds in bringing the October bill to the House floor, it should be fought with strengthening amendments in an "open process."

"Any strategy of letting a weak bill go through now to improve it later is probably not going to work, because you're going to be operating from weakness," said David Baker, political director of Friends of the Earth. "That's a strategy not in the best interest of public health."

The firm opposition of Baker and other factions has been labeled

"kamikaze tactics" by fellow environmentalists.

"It's not a rational position," said Lawrie Mott, senior scientist of the National Resources Defense Council. "If anybody can throw away this possibility of getting FIFRA reform in the hope of getting a better bill later, that's very irresponsible. It doesn't gain any protection of the environment or public health."

In support of the Waxman-Dingell proposal, Mott said a House floor fight could weaken the bill by opening it to amendments by the pesticide industry. Moreover, it might discourage the Senate from focusing on pesticide revision for fear of a "wide-open free-for-all" in that chamber, she said.

"If Dingell and Waxman can make a deal with the Agriculture Committee," she said, "we gain much more than we can on the House floor."

Congressional sources said the environmentalists' infighting impedes their mission by sending conflicting signals to lawmakers.