By JOHN M. BRODER and MICHELINE MAYNARD, The New York Times

WASHINGTON, Nov. 30 — Congressional negotiators reached a deal late Friday on energy legislation that would force American automakers to improve the fuel efficiency of their cars and light trucks by 40 percent by 2020.

The proposal, which would require automakers to achieve 35 miles per gallon on average, is similar to a measure that was passed in the summer by the Senate but was bitterly opposed by the auto companies, who argued they did not have the technology or the financial resources to reach that goal.

The auto companies gave up their long-held opposition to fuel- economy increases not long before the Senate version was passed, but proposed a much weaker alternative. In recent weeks, the chief executives of General Motors, the Ford Motor Company and Chrysler visited Capitol Hill in an effort to fend off a stronger measure, but the compromise announced Friday showed those efforts had little effect.

The compromise emerged after days of difficult negotiations between House and Senate members and their staffs. The final deal was hammered out by the two main antagonists, the speaker of the House, Nancy Pelosi, Democrat of California, and Representative John D. Dingell, the Michigan Democrat who is the auto industry’s most effective advocate on Capitol Hill.

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