Updated from 7:51 a.m. EST

President Bush's ambitious plan to overhaul the Medicare system passed the Senate Tuesday and was headed for his desk for a signature. Meanwhile, a vote on another piece of key legislation, a plan to give the U.S. energy industry billions of dollars of government subsidies, must wait until January.

Senate leadership maneuvered past two efforts to block passage Monday of the Medicare bill, which earmarks $400 billion over 10 years to add a prescription drug benefit for the elderly and expand the number of health insurance providers available under the 38-year-old entitlement.

Several Democrats joined with most of the chamber's Republicans in beating back a filibuster threat Monday, then teamed up to win a roll-call vote that could have snagged the legislation on a procedural technicality having to do with the budget-appropriations process.

The measure passed the House over the weekend.

"Today is a historic day and a momentous day," said Senate majority leader Bill Frist Monday. "Seniors have waited 38 years for this prescription drug benefit to be added to the Medicare program. Today they are just moments away from the drug coverage they desperately need and deserve."

Senate leadership was less successful navigating around opponents of the other major proposal of President Bush's first term, a bill that would spend $31 billion over 10 years to overhaul the energy industry and revamp the power grid, whose failure led to the country's worst-ever blackout in August.

The bill's backers reportedly are two votes shy of pushing it through and must now wait until after the winter recess to seek passage again. The bill got hung up on a provision that would indemnify the manufacturers of a fuel additive in the event of ground water contamination.

Other parts of the bill would grant incentives for cleaner-burning coal, nuclear energy and various alternative energy sources. It would impose reliability standards for companies that own the electricity grid.