Senate discussions are expected to continue Tuesday about the $2 billion extension of the popular "cash for clunkers" auto rebate program.

Senate Democrats are struggling to win over enough reluctant Republicans to approve the program, which has picked up support from three lawmakers who had reservations about the fuel efficiency of vehicles being bought. Data released by the administration shows the new vehicles purchased under the program were 61 percent more fuel efficient than the trade-ins.

That helped sway Democrats Dianne Feinstein of California and Chuck Schumer of New York, and Republican Susan Collins of Maine.

The White House says the incentives are unlikely to continue into the weekend if the Senate fails to approve the extra funding already passed by the House.

Carmakers say the program has helped boost sales.