The Senate is scrapping plans for an 18-month extension of surface transportation law and is now working instead on a six-month extension, a Democratic aide and industry officials confirmed Friday.

Barbara Boxer , D-Calif., and James M. Inhofe , R-Okla., — the chairwoman and ranking member of the Environment and Public Works Committee — were unsuccessful in persuading their colleagues to allow quick passage of an 18-month extension of the 2005 surface transportation law.

An industry official said the senators realized they would have trouble moving the administration-backed 18-month extension, so they acquiesced to a shorter term bill.

The six-month extension was touted by George V. Voinovich , R-Ohio, who said he would have blocked the 18-month bill. He says the highway and transit programs are too important to the economy to wait more than a year to fix, and he sought the shorter extension to put pressure on Congress to enact a full, multi-year reauthorization next year.

A shorter extension would be a victory for proponents of long-term transportation legislation such as the six-year, $500 billion plan being pressed by House Transportation and Infrastructure Chairman James L. Oberstar , D-Minn.

But a six-month extension would still leave the Senate at odds with the House, which passed a three-month extension Sept. 23. Oberstar has adamantly opposed any extension beyond the end of the year, because he wants to force Congress to take up a multiyear highway bill early in 2010.

Programs are being kept afloat within a one-month fiscal 2010 stopgap spending measure that expires Oct. 31. Congress is poised to pass another one of those measures soon, while appropriators finish the fiscal 2010 spending bills.