With a highway construction bill (search) making little progress and shadowed by a veto threat, the House moved Wednesday to extend the current highway program through June.

The 421-0 vote in the House came as the Senate struggled to complete work on its $318 billion bill to fund highway, public transit and safety programs through 2009. The last six-year bill, funded at $218 billion, expired in 2003, but has been extended until the end of February.

Senate leaders hope to finish their bill by week's end. But the legislation, viewed by many as the most important that Congress will take up this year, faces an uncertain future.

Some in the House are demanding more spending. From the White House came a statement Wednesday that spending levels in the Senate bill were too high and the measure would be subject to a presidential veto.

"We'll probably hit a few more potholes along the way," said Sen. Jim Jeffords (search), I-Vt., one of the Senate sponsors.

Senators agreed they could not get a bill to the president by March 1. But some expressed dismay at the House action.

"You lose this year's construction season" by funding projects at the old level, said Sen. Kit Bond, R-Mo. He added that "it isn't going to get any easier four months from now," closer to the election, to pass a bill.

The administration, citing the need for fiscal restraint, has recommended a $256 billion transportation bill. The White House statement raised the threat of a veto of any bill that goes above that spending level by raising taxes or increasing the deficit.

The House Transportation and Infrastructure Committee (search) has backed a $375 billion measure, but GOP leaders have rebuffed the committee's proposal to help pay for that total by raising the federal gas tax, now at 18.4 cents per gallon.

Federal highway money comes entirely from the highway trust fund, which is derived from that tax.

"Right now we're going to kick the can down the road a little bit and hope that people come to their senses and do the $375 billion bill," said Rep. Jim Oberstar of Minnesota, top Democrat on the House Transportation Committee.

The Senate planned a vote Thursday on ending the delaying tactics by GOP conservatives who agree with the White House that the bill is too expensive.

But many Republicans were leaning in the other direction. Sen. James Talent, R-Mo., said the $375 billion sought by the House was necessary if the country is to "start paying back the transportation deficit" while creating hundreds of thousands of jobs.

He noted that 32 percent of the nation's roads are in poor or mediocre condition, that congestion causes $67 billion in wasted time and fuel every year, and that Americans pay $49 billion extra in car repairs every year because of bad roads.

Talent, joined by Sens. Ron Wyden, D-Ore., Norm Coleman, R-Minn., and Jon Corzine, D-N.J., was proposing a $56 billion initiative that would raise road money through the sale of bonds. He described it as a way that companies and individuals could invest directly in America's future.

The administration extended the veto threat to any funding through bonding.

Also Wednesday, the Senate rejected a measure intended to force states to toughen their seat belt laws. Lawmakers said it was up to state legislatures to tell drivers to buckle up.

The amendment would have taken away federal highway money from states that did not enact primary seat belt laws or which failed to reach a seat-belt use rate of 90 percent. It was defeated 56-42.

Primary seat belt laws, enacted in about 20 states, allow police officers to stop drivers whose only violation is failure to wear a seat belt.

Sen. John Warner, R-Va., sponsor of the amendment with Sen. Hillary Rodham Clinton, D-N.Y., said that more than half the nearly 43,000 people killed in vehicle accidents in 2002 were not wearing seat belts. He cited government estimates that 9,200 of those deaths might have been prevented if safety belts had been used.

"No one disputes this legislation will save lives," Warner said.

But opponents objected to withholding federal highway money from states not meeting the federal standards. "This approach is essentially federal blackmail by Congress," Bond said.