WASHINGTON -- A leading lawmaker seemed willing today to pare back a dramatic hike in automotive fuel economy standards, but car makers still say the proposed rules are too aggressive.

The current Senate Energy Bill requires automakers to average 35 miles per gallon by 2020 and then face yearly 4 percent increases through 2030, ending up with a combined 52 mile-per-gallon requirement by 2030.

Sen. Dianne Feinstein, D-Calif., today was negotiating to drop the 4 percent annual increases between 2021 and 2030, The Detroit News has learned from several environmental groups and auto lobbyists.

Also under consideration are proposals to soften the mandate that 80 percent of vehicles be made to run on flexible fuels. Foreign automakers don't have many -- if any -- current vehicles that run on flexible fuels like E85 ethanol.

Auto company officials weren't placated.

"This is a ploy to show 'look how generous we are.' The bill is still unattainable," said one senior domestic auto official.

Automakers have backed an alternative dubbed "Pryor-Bond-Levin" that would offer a softer increase -- at least 36 miles per gallon for passenger cars by 2022 and 30 miles per gallon for light trucks by 2025. It only requires 50 percent of vehicles to run on alternative fuels and allows automakers to count hybrids as alternative vehicles.

Sen. Barbara Boxer, D-Calif., said talks were underway to "meld the two approaches together."

Several Republican aides said it now appears automakers don't have the votes to pass the Pryor-Bond-Levin bill and at the very least it is in serious trouble.

The Pryor-Bond-Levin bill is opposed by Nissan Motor Co. for a number of reasons and their opposition has thrown into doubt the support of Republican senators from states where Nissan has a heavy presence. Nissan doesn't like a provision that would retain small car production in the United States -- a provision demanded by the United Auto Workers.

Both Tennessee senators, Lamar Alexander and Bob Corker, are expected to vote against the bill, and Mississippi's senators, Thad Cochran and Trent Lott, are undecided.

As issues of contention mount, a vote may be delayed on both the Levin alternative and the Senate bill until next week.

Sen. Barbara Mikulski, D-Md. is another key swing vote, among the roughly dozen undecided senators. Sens. Mark Pryor, D-Ark., and Debbie Stabenow, D-Mich., both spoke at length with Mikulski following a Senate Democratic lunch yesterday that focused on energy.

The senators sought to convince Mikulski to support them. She hasn't taken a public position, her spokeswoman, Melissa Schwartz said today.

You can reach David Shepardson at (202) 662 - 8735 or dshepardson@detnews.com.