As House Republicans prepared to release a spending proposal intended to overhaul the federal transportation system, Senate Democrats on Thursday rushed to complete a bipartisan effort to end a stalemate that has undermined transportation programs for almost three years.

The flurry of activity on the Senate side came a day after U.S. Transportation Secretary Ray LaHood said that differences between House and Senate proposals presented “a pretty big gulf to overcome” and that it was unlikely a bill would win approval in this election year.

His gloomy appraisal set off a flurry of phone calls on Capitol Hill on Thursday morning, with LaHood hearing from Sen. Barbara Boxer (D-Calif.), whose public works committee unanimously approved a two-year transportation bill in November.

Boxer said that she received a call from Senate Majority Leader Harry M. Reid (D-Nev.) and that he assured her that two other Senate committees — commerce and banking — would take action on the bill next week. Portions of the bill need the approval of the other committees.

“That means that by the end of next week all the [Senate] committees will have done their jobs,” Boxer said in a meeting with reporters.

She said the bill will reach the Senate floor before transportation funding expires March 31. The last long-term funding bill ran out in 2009, and transportation planners have been hamstrung by uncertainty during eight temporary extensions.

The House bill is expected to be distributed to transportation committee members Friday. The bill, almost 1,000 pages long, is a translation of concepts outlined last year by the committee chairman Rep. John L. Mica (R-Fla.).

Mica contends that a five-year spending plan will better address the desire of federal and state transportation administrators who want some guarantee of long-term funding before they launch major highway or transit projects.

On Thursday, Boxer urged the House not to “load this bill with very controversial items.”

She said members of her committee made significant concessions to reach a bipartisan compromise. “What we did in the Senate was a model of bipartisanship,” she said.

Transportation funding has been stalled since the last major bill expired because the Highway Trust Fund no longer provides the steady stream of revenue needed to fund the transportation system. The trust fund relies primarily on money from the 18.4-cent-per-gallon federal gas tax, revenue that has declined as engine efficiency has improved.

The two-year Senate bill is $12 billion short of the amount needed to fund a proposal that would allocate $80 billion for surface transportation and an additional $29 billion for transit and transportation safety. Finance Committee Chairman Max Baucus (D-Montana) has indicated that his committee can find the money to bridge that gap.

House Republicans have talked of augmenting trust fund revenue for their five-year, $260 billion bill by expanding domestic oil production. Boxer said Thursday that if the new production comes from areas already approved for drilling she would not object.

“If they start saying they want to drill in states that don’t want it,” she said, “. . . that’s very controversial. I’ve said many times to Chairman Mica, stay away from controversy.”