The two television ads are almost indistinguishable. In both, former Bain Capital executive Robert C. Gay tells the tale of Mitt Romney’s role in leading a search for Gay’s missing daughter, interspersed with footage of New York and flashes of Romney.

“Mitt’s done a lot of things that people say are nearly impossible,” Gay says in the two spots, his voice choking with emotion. “But for me, the most important thing he’s ever done is to help save my daughter.”

The only substantive difference between the two commercials, in fact, is their sponsors: One was broadcast in 2007 by Romney’s presidential campaign; the other was aired this month by Restore Our Future, a super PAC supporting his 2012 candidacy.

The commonalities have set off a sharp legal debate over the boundaries of campaign coordination rules and have prompted a Washington watchdog group to file a complaint with the Federal Election Commission. Restore Our Future says the ad is perfectly legal.

The dispute marks the latest row over the influence of super PACs, independent groups that can raise unlimited money but are barred from direct coordination with campaigns. The groups, which were formed in the aftermath of favorable court rulings, have become a major factor in the GOP primaries.

The question at the heart of the dispute is whether use of five-year-old footage amounts to an unlawful contribution to Romney’s 2012 campaign. The Campaign Legal Center, a nonpartisan group that favors stronger regulation of campaign-finance activities, says in its complaint that any “republication” of campaign materials, even from a previous election, is considered an in-kind contribution under FEC rules.

If so, the new version of the advertisement would be considered illegal because super PACs are not allowed to contribute to candidate campaigns.

“Here we have an ad that was clearly, undeniably prepared by a candidate or agent of a candidate, and this group is financing republication of that material,” said Paul S. Ryan, associate counsel at the legal center. “That is considered a contribution.”

But Charlie Spies, a lawyer with Clark Hill who serves as Restore Our Future’s treasurer, said the complaint is without merit. He said that the group purchased the rights to the footage from the owner, Cold Harbor Films of Alexandria, and that there was no coordination or contact with the Romney campaign.

“The Campaign Legal Center imagines campaign-finance violations around every corner,” Spies said. “Restore Our Future has fully complied with all FEC regulations in purchasing archival footage for use in creating our advertisements.”

Although the two commercials appear nearly the same, a number of details are different, including imagery used to depict New York and the specific shots showing Romney. The narration and visual imagery of Gay, however, are identical.

Gay, a former managing director at Bain Capital, which Romney co-founded, is chief executive of Huntsman Gay Global Capital, which he co-founded with the father of Jon Hunstman Jr., a former Romney rival for the GOP nomination. Gay’s 14-year-old daughter had gone missing for several days in 1996 after taking the drug ecstasy at a rave party; she was eventually located in New Jersey after a boy who was with her called authorities.

The questions raised in the Restore Our Future case are fairly novel, and campaign-finance lawyers disagree both about the legality of the new commercial and how the FEC might rule. The commission, which has been mired in partisan gridlock for years, deadlocked on a separate case in January about smaller snippets of recycled footage used in an ad by the American Crossroads conservative group.

Brett G. Kappel, a lawyer with the firm Arent Fox, said the issue of timing would probably be important to the FEC, given the gap between the original ad and the new one. In addition, he said, the American Crossroads case indicates that the panel is likely to deadlock in any case.

“I’ve never seen them bring an enforcement case based on campaign materials used in a prior campaign — even a prior campaign for the same office,” Kappel wrote in an e-mail. “ . . . I would certainly expect the commission to deadlock on a case involving campaign materials from a race that was held over four years ago.”

Richard L. Hasen, an election-law professor at the University of California-Irvine, said he views the super PAC ad as “a pretty clear violation of the rules” but said the FEC is unlikely to act on the complaint until after the election, if at all.

“It’s not going anywhere anytime soon,” Hasen said. “By the time this is decided, the election will be over and Restore Our Future could have already disappeared. There’s no real accountability for this type of violation.”