WASHINGTON — The Senate is set to take up legislation to keep federal highway money flowing to states, with just three days left before the government plans to start slowing down payments.

The House passed a $10.8 billion bill last week that would pay for highway and transit aid through the end of May if transportation spending is maintained at current levels. Under a schedule outlined by Majority Leader Harry Reid, D-Nev., the Senate would take up that bill today.

But senators who say the House bill uses budgetary gimmicks to pay for roads and bridges or who want to force Congress to act before the end of the year on a long-term plan to pay for transportation programs are expected to offer amendments. If any amendment passes, it would alter the underlying House bill and set up an 11th-hour showdown between the House and Senate on how to resolve the differences between their bills.

The Transportation Department says by Aug. 1 the federal Highway Trust Fund will no longer have enough money to cover promised aid to states, and the government will begin to stretch out payments. Congress has kept the trust fund teetering on the edge of bankruptcy since 2008 through a series of temporary fixes because lawmakers have been unable to find a politically acceptable, long-term funding plan.

Without action from Congress, the balance in the fund is expected to drop to zero by late August or early September. Some states already have cut back on construction projects because of the uncertainty.