Senator Clinton’s campaign is charging Senator Obama with hypocrisy for denouncing independently funded advertising campaigns which supported his opponents in Iowa but saying little about similar efforts being mounted now on his behalf in Ohio.

However, Mrs. Clinton’s own position on the appropriate role for so-called 527 organizations is murky, a fact which complicates her attempt to tarnish Mr. Obama concerning the issue.

“In Iowa, he criticized this kind of spending but in Ohio he is largely silent,” a spokesman for Mrs. Clinton, Howard Wolfson, said. “Senator Obama has a pattern of making promises, making statements that are not backed up by his actions….That is not change you can believe in.”

The Clinton campaign’s salvo against Mr. Obama came in response to what the New York senator’s aides said was a plan by a supermarket union, the United Food and Commercial Workers, to spend hundreds of thousands of dollars on pro-Obama television advertising in Ohio between now and the March 4 primary. A spokeswoman for the UFCW, Jill Cashen, confirmed late last night that group funded by union members will roll out TV ads across Ohio tomorrow which underscore the Illinois senator’s commitment to universal health care and other issues.

A spokesman for Mr. Obama said the Illinois senator has consistently urged independent groups to steer clear of the presidential race. “While Senator Clinton has benefited from more than $5 million in spending from outside groups and said nothing, Senator Obama has long said that he would prefer those who want to support him do it directly through the campaign,” the spokesman, Tommy Vietor, said.

In December, Mr. Obama sent a letter to a purportedly independent pro-Obama organization based in California, Vote Hope, urging it to desist from advertising and fund-raising. Vote Hope and a related group, PowerPAC.org, ignored the request. On Thursday, Powerpac reported it had spent more than $150,000 on a pro-Obama mailing to voters in Texas, who also vote March 4. Mrs. Clinton’s allies have also organized a so-called 527 group, American Leadership Project, which plans to air TV ads in Ohio. Mr. Wolfson said yesterday the group had no connection to the campaign.

The outside organizations, which are called 527s or sometimes 501(c)4s after the section of the tax code under which they were organized, are attractive to wealthy donors because the groups do not generally observe the rules of federal political action committees, which can accept only $5,000 from each donor each year.

In 2004, such groups spent an estimated half a billion dollars on activities related to federal elections, including television ads and get out the vote efforts. A top Democratic donor, George Soros, gave about $25 million to groups including the Media Fund and America Coming Together, which worked to help the Democratic nominee, John Kerry. A top Republican donor, Robert Perry, gave more than $8 million to groups such as Progress for America, which touted President Bush’s record, and Swift Boat Veterans for Truth, which questioned Mr. Kerry’s record in the Vietnam War. Mr. Bush, and the likely Republican nominee this year, Senator McCain of Arizona, denounced the 527 efforts as illegal and even went to court to try to shut the groups down. The positions of Mrs. Clinton and Mr. Obama on the issue are less clear.

In interviews in August 2004, Mrs. Clinton was asked whether the 527 committees should be banned. “I have no problem with eliminating any group that is misusing their financial position to spread inaccurate falsehoods,” she told CNN.

“We’re going to have to look at this whole 527 issue. Obviously, too much money is chasing too many issues that, unfortunately, are being distorted. I mean, if there was some standard of accuracy, you know, we wouldn’t be here talking about it. But there isn’t,” she told NBC that summer.

Asked if both sides should agree to a “truce” taking all independent ads off the air, Mrs. Clinton said, “I’d be for that. I don’t think that you’ll get agreement on that because there’s too much, you know, intensity and too much money.”

Last fall, Mr. Obama answered a questionnaire from a coalition of civic and public interest groups, the Midwest Democracy Network, by saying that he favored imposing the $5,000 limit on 527s “organized primarily to affect federal elections.”

Since 2005, some in Congress, mostly Republicans, have moved to make the law clear that such groups had to observe the $5,000 limit and other rules.

A longtime adviser to Mrs. Clinton now overseeing her superdelegate recruiting team, Harold Ickes, was a leading opponent of reining in 527s. He warned that doing so could reduce voter registration and get-out-the-vote efforts in minority communities. Mrs. Clinton never took a clear position on the legislation.

The effort to impose limits on 527s faltered due in large part to opposition from the nonprofit sector and to a sense that new 527 activity was being restrained by $3 million in penalties imposed on organizations alleged to have violated the law in 2004.

Independent expenditures by unions are not entirely synonymous with those by 527 groups, though some 527s have tapped into union-backed political funds. Asked yesterday if Mrs. Clinton believes 527s funded with large donations are beneficial to the system and whether they should be legal, Mr. Wolfson said, “I’m not making a value judgment about it, if they are doing it within the law it is legal.”

“We are more concerned about what Senator Obama said and doesn’t say about this than anything else,” he said.