Washington — A deal on a toxic-chemcial regulation bill promoted by Sen. David Vitter, R-La., brings more Democratic senators on board with the measure, Vitter’s Democratic co-sponsor of the legislation said Monday, on the eve of committee action on the proposal.

The update of the 1976 Toxic Substances Control Act is scheduled to come up Tuesday before the Senate Environment and Public Works Committee. Vitter and his fellow Republicans hold the majority on the committee, but the support of Democratic members Cory Booker, of New Jersey, Jeff Merkley, of Oregon, and Sheldon Whitehouse, of Rhode Island, will strengthen the bill’s chances on the Senate floor.

Backers of the bipartisan update effort lead by Vitter and Sen. Tom Udall, D-N.M., say the proposal represents a significant and long-overdue overhaul of the 1976 law.

TSCA was intended to provide for the federal Environmental Protection Agency to protect Americans from exposure to toxic or harmful substances in clothing, furniture, cleaning products and elsewhere in the environment. But chemical manufacturers and environmentalists agree the law is outdated and largely ineffective. It largely exempted chemicals already in the marketplace from regulation, and a court decision that struck down a ban on asbestos weakened the law. Of the thousands of chemicals in commercial use today, nine are regulated under TSCA.

Several states have stepped into the breach to regulate chemicals, and the status of future state enforcement efforts is a key point of contention in the TSCA debate. In Louisiana, home to the second-largest chemical manufacturing industry in the nation (after Texas), state laws regulate the presence of mercury and lead in consumer products.

The Udall-Vitter legislation would subject many more chemicals to regulation, set minimum requirements and timelines for EPA testing, establish a fee system to finance the program and address major weaknesses in TSCA revealed by the court decision in the asbestos case.

But the version heard by the committee last month drew criticism from Democratic senators and environmentalists, particularly over its pre-emption of state regulations. The deal announced Monday on Udall’s web site, and including the three Democratic committee members, would offer more protection for separate state efforts to regulate the chemicals.

Chemical industry groups have supported the Udall-Vitter legislation. Numerous environmental groups have opposed it, although the Environmental Defense Fund has endorsed it.