Washington ? The Senate voted Wednesday to halt the administration’s effort to rewrite decades-old rules on overtime pay, risking a veto showdown with President Bush and heeding labor’s claims that the changes would harm millions of workers at a time of economic uncertainty.

The 54-45 vote marked a rare defeat for business interests in the GOP-controlled Congress and left the fate of the emerging Labor Department regulations unclear. The House backed the new rules this summer, and congressional negotiators will have to resolve the issue.

“The Bush administration proposal is not only anti-worker and anti-family, it is bad economic policy,” said Democratic Sen. Tom Harkin of Iowa, who led the assault on the regulations.

“It will take money out of the pockets of hardworking Americans and will not create one new job.”

Labor Secretary Elaine Chao defended the effort as a bid to “strengthen overtime protections for workers” by extending overtime eligibility to 1.3 million low earners who now lack it. “The regulatory process should move forward to benefit workers,” she said.

Democratic opponents said their plan would not interfere with parts of the rules extending overtime protection. They took aim at sections that would strip other workers of eligibility they have long enjoyed. The precise number was a matter of dispute — an estimated 800,000 by administration allies, and as high as 8 million by Harkin’s estimate.

The vote came as the Senate labored to complete work on a $137.6 billion spending bill for health, education and labor programs for the fiscal year beginning on Oct. 1.