WASHINGTON — A transportation bill that House Republican leaders promote as the centerpiece of their job-creation agenda is instead turning into one of their biggest headaches.

Opposition by tea party conservatives who want to get the federal government out of transportation programs and hand them over to the states has helped stall the bill.

The House and Senate are heading toward a showdown next week that could result in a cutoff of federal highway and transit aid to states just as the spring construction season gets under way.

The government's authority to spend money from the trust fund that pays for transportation programs expires on March 31.

Republicans are pressing for a 90-day extension of programs, but Senate Majority Leader Harry Reid says he's "not inclined" to go along.