WASHINGTON — In his fight to repeal a federal gun law, Mayor Bloomberg has flown across the country, spent millions in televised campaign-style ads, raised his national profile, and sparked interest in a possible presidential run.

But in Congress, he’s hardly changed anyone’s mind.

If anything, support in the powerful House Appropriations Committee for the so-called Tiahrt Amendment, which restricts access to gun trace data, has grown since it passed by a one-vote margin when it was first added to a spending bill in 2003. The committee last week rejected on a voice vote an attempt to repeal it entirely, and an effort to scale it back failed on a vote of 40–26. The result follows Senate approval of the measure last month and virtually guarantees that it will pass the full Congress.

For the mayor, the issue that has helped to vault him onto the national stage has also dealt him a resounding legislative defeat, which is now drawing criticism for his political strategy and raising questions about how successful he can be at effecting change in Washington.

Mr. Bloomberg initially reached out to supporters of the measure, even meeting earlier this year with its chief sponsor, Rep. Todd Tiahrt, a Republican of Kansas. Unsatisfied with the answers he received, however, the mayor quickly shifted to a more confrontational tack, including buying television ads through his anti-illegal gun coalition that accused some committee members of protecting criminals over the police. In public statements on the bill, the mayor has vowed repeatedly to hold lawmakers accountable for their votes during the next election, a statement that many view as a threat to spend his considerable wealth to campaign against them.

In interviews yesterday, congressional Democrats who support the mayor’s position expressed dismay at his strategy, saying it was overly brash and aggressive.

“Right issue, wrong approach,” a Democratic committee member who voted with the mayor, Rep. Jose Serrano of the Bronx, said. He criticized the mayor’s ad campaign as threatening. “I think the mayor, every so often, forgets that we live … in a legislative world.”

Mr. Serrano added: “You have to be diplomatic, persuasive.”

Others said it never stood a chance. “We don’t have the votes. We never really had the votes,” a Democratic congressman who represents parts of Brooklyn and Queens, Anthony Weiner, said. Mr. Weiner made a failed bid for mayor in 2005 and is likely to run again in 2009.

Yet Mr. Bloomberg probably knew that as well. In a statement after the vote, he expressed “profound disappointment” and said he had been “hopeful” that the committee would stand up to the special interests. But he did not say he was surprised, and a mayoral spokesman refused to say yesterday whether City Hall had expected a different result.

Although the mayor and his allies insist that the issue is not about gun control, it has attracted the attention of the National Rifle Association, which aggressively mobilized its leadership and its supporters in Congress to oppose Mr. Bloomberg. City officials contend that the Tiahrt Amendment ties the hands of police by restricting the use of gun sales data, while the NRA has tried to advance a similar argument in opposition, saying the use of the data would expose and endanger police officers working in undercover investigations.

Both supporters and critics of Mr. Bloomberg’s stance on the Tiahrt Amendment acknowledge that the mayor has succeeded in elevating himself nationally even as he has failed to change the law. “I don’t know if that’s what his motives were, but it couldn’t hurt,” a Democratic ally on the Appropriations Committee, Rep. Steve Israel of Long Island, said.

Instead, Mr. Bloomberg appeared to alienate the chairman of the committee, Rep. David Obey, a Democrat of Wisconsin, when lobbyists for the mayor threatened to run negative ads against him if he didn’t oppose the amendment, according to a statement Mr. Obey made before the vote last week. The mayor’s office denies the account. “No one was threatened,” a spokesman, Jason Post, said yesterday. Mr. Tiahrt said yesterday that the outcome should teach Mr. Bloomberg “a lesson” about working in Washington.

Yet the issue could cut both ways for the mayor should he seek the White House, playing right into his message that Capitol Hill is beholden to special interests like the gun lobby and that while he could not force change as a mayor, he could as a president.

Lawmakers said Mr. Bloomberg could do well pushing the gun issue in urban centers where his core constituency is likely to be, but not in rural areas heavily populated by gun owners. As Mr. Serrano, the Bronx Democrat, put it: “It’s certainly a good issue to run. It’s also a good issue to get his head handed to him.”

City officials yesterday declined to discuss the mayor’s strategy in fighting the Tiahrt Amendment. When asked what Mr. Bloomberg’s next move would be and whether he would carry out his pledge to oppose lawmakers who voted against him, Mr. Post said only: “Stay tuned.”