WASHINGTON — Federal election regulators refused to ease limits on political advertising yesterday, blocking an effort to let interest groups run radio and television ads mentioning elected officials within weeks of an election.

The Federal Election Commission voted 3-3 on a proposal that would have allowed such ads as long as they addressed public policy issues and did not promote, support, oppose or attack a sitting member of Congress. Supporters of the change said they wanted to strike a balance between campaign-ad restrictions and constitutional free-speech guarantees.

The measure failed with the commission’s three Democrats voting against the proposal and the three Republicans backing it.

With 70 days left before the general election, the change could have let loose a wave of unrestricted ad spending in the weeks leading up to Election Day. The vote lets stand a provision in the 2002 McCain-Feingold campaign-finance law that requires independent groups to limit the contributions and to disclose the donors of money used to pay for ads that run within 30 days of a primary or 60 days of a general election.

The commissioners agreed that ultimately they would have to consider whether to add an exemption to the advertising provision, but split 3-3 again on a proposal to start that process immediately.

Three federal lawsuits challenging that section of the 2002 law, known formally as the Bipartisan Campaign Reform Act, are wending their way through the courts. The Supreme Court is not expected to address the legal issues until next year.

Democratic Commissioners Ellen Weintraub and Steven Walther said they wanted to wait for the high court to rule before adopting any exemptions to the law. Republicans on the commission argued that such a delay could leave the issue unresolved well into the 2008 presidential nomination contests.

“It’s important that the agency squarely address the issue and provide finality one way or another,” FEC Chairman Michael Toner said. “It is clear that right now there isn’t a majority of the agency to go forward.”

Advocates of the change covered the political spectrum, from the U.S. Chamber of Commerce to labor unions to the ACLU to a number of smaller nonprofit advocacy groups. They said the law not only restricted campaign advertising but also prohibited interest groups from voicing their views on legislation before Congress.

Commissioner Hans von Spakovsky, a Republican nominee and the author of the proposed change, argued that the BCRA aimed to prevent corruption or the appearance of corruption at the intersection of money, legislation and elections.

“When you restrict the ability of citizens in legislative decision-making, that’s when you get corruption,” he said.

Critics, including the congressional authors of the 2002 law, argued that clever ad writers could still use those limitations to promote or criticize a candidate for office.

“This would have meant a return to the era before campaign-finance reform, when special interest groups were able to exert enormous influence on our electoral process by funding attack ads with unlimited amounts of soft money,” said Rep. Martin Meehan, D-Mass. Meehan helped write the BCRA with Rep. Christopher Shays, R-Conn., and Sens. John McCain, R-Ariz., and Russ Feingold, D-Wis.

Interest groups can run ads that name candidates and advocate causes as long as the ads are paid for by a political action committee. PACs are limited in the size of contributions they receive and must disclose their donors to the public.

“It’s not as if the corporate vehicle and the union vehicle is completely shut out from the debate during this period,” Walther said.