WASHINGTON — House Republicans renewed their election-year assault on President Barack Obama’s health care law Thursday, their opposition undimmed just days after Obama celebrated news that more than 7 million Americans had signed up for coverage under the law.

The GOP-led chamber voted 248-179 to change the law’s definition of full-time work from 30 hours a week to 40 hours a week. The result would be that fewer workers would get employer-sponsored health coverage and hundreds of thousands more people would be uninsured, according to the Congressional Budget Office.

Republicans, backed by the Chamber of Commerce and other business groups, said the change would restore the traditional definition of full-time work while providing needed relief to businesses that are struggling with increased costs from the health care law. Businesses say they are being forced to cut worker hours, limit full-time jobs and drop health coverage because of the law, which requires businesses with 50 or more full-time workers to provide health coverage or pay penalties.

It was the House GOP’s 52nd vote to change, repeal or otherwise uproot Obama’s health law, and the measure faced certain death in the Democratic-controlled Senate. Eighteen Democrats joined with all Republicans in approving the bill, named the Save American Workers Act of 2013.

In rancorous debate on the House floor, Democrats accused Republicans of being obsessed with attacking the health law, while Republicans ridiculed Democrats for trying to change what they called a commonly understood definition of full-time work. “We all know 30 hours isn’t full time but that’s what Obamacare says,” said Rep. Tim Griffin, R-Ark. “Even in France a full-time job is 35 hours”

Democrats said the law’s 30-hour definition for a full-time workweek was meant to make it harder for employers to avoid covering full-time workers by slightly reducing their hours. Changing the definition would make the requirement meaningless because employers could simply skirt it by knocking full-time workers down to 39-and-a-half hours a week, they said.