WASHINGTON — Opening a new rift with his successor at City Hall, Mayor Giuliani has endorsed a gun law that Mayor Bloomberg has spent the better part of a year trying to get repealed.

In his appearance Friday before the National Rifle Association, the former mayor highlighted the Tiahrt amendment in describing the shift in his view on gun rights, saying the law was “sensible” and that law enforcement was “comfortable” with it.

The amendment, which has been added to congressional spending bills since 2003 with the backing of the NRA, places restrictions on how gun trace data can be used, and it lies at the center of the national campaign Mr. Bloomberg has waged on illegal guns.

The Tiahrt amendment was one example Mr. Giuliani cited as part of his bid to square his past support for gun control laws with his current embrace of the Second Amendment, an evolution he described during a speech Friday as he tried to win over skeptical NRA members, an influential Republican constituency.

“You’ve also had, as an intervening fact, the Tiahrt amendment, which I think is a sensible one, a sensible division,” he said. “It gives law enforcement the ability to get information. Law enforcement is comfortable with it.”

The legislation is named for its original sponsor, Rep. Todd Tiahrt, a Republican of Kansas.

When asked about the bill at a press conference a day earlier, Mr. Giuliani said he would have to look into it. A campaign spokeswoman said yesterday that Mr. Giuliani’s statement to the NRA speaks for itself.

The Republican presidential hopeful also used the NRA appearance to distance himself from the lawsuit he initiated as mayor against gun manufacturers, which the Bloomberg administration is still litigating in court. “That lawsuit has taken several turns and several twists that I don’t agree with,” he said. His remarks were a far cry from his tone as mayor, when he likened NRA members to “extremists.”

Mr. Giuliani’s position on the Tiahrt legislation puts him in direct conflict with Mr. Bloomberg, who has said a vote for the amendment is tantamount to “voting to put guns in the hands of criminals.”

He has argued that the bill ties the hands of law enforcement and prevents the city from stopping the flow of illegal guns onto its streets. Underscoring the signifigance of the policy difference is the possibility that Mr. Bloomberg will mount his own campaign for the presidency next year. While the two mayors once shared similar views on social issues like gun control, abortion, and gay rights, Mr. Giuliani has shifted distinctly to the right in some areas in his bid to win the Republican nomination.

On Tiahrt alone, Mr. Bloomberg has crisscrossed the country railing against the bill, building a bipartisan coalition of more than 200 mayors who have rallied around its abolition. The effort has involved an intense lobbying push, and the coalition has run television ads in the congressional districts of key lawmakers on the House Appropriations Committee. The mayor has even threatened to campaign next year against House members who vote for the bill. Whether Mr. Bloomberg will do the same to Mr. Giuliani is unclear.

Asked for reaction to Mr. Giuliani’s support for the Tiahrt amendment, the mayor’s chief spokesman, Stuart Loeser, said: “No comment.”

The NRA and other supporters of the legislation contend that releasing data restricted by the Tiahrt amendment could compromise ongoing law enforcement investigations. The group also says the city wants the data only so it can pursue civil lawsuits to put gun dealers out of business.

On that front, City Hall has declared a partial victory in recent weeks following the decision last month by the federal Bureau of Alcohol, Tobacco, Firearms, and Explosives to release a trove of aggregate gun trace data covering the year 2006. The move follows the city’s failure to get the Tiahrt amendment removed from this year’s spending bills in Congress.

The bureau had not released such data since the Tiahrt amendment was enacted, although there is disagreement about whether the law specifically prohibited making it public.

“We welcome the policy shift by ATF,” Mr. Loeser said, adding that the city hoped the agency will commit to sharing that kind of information going forward.

The ATF’s assistant director for governmental and public affairs, Larry Ford, said the bureau decided to release the data on its Web site after determining that they would not compromise law enforcement investigations or undercover personnel.

“We saw there was a demand for that kind of information,” he said.

While they are pleased with the move, city officials said it would not stop their efforts to kill the Tiahrt amendment, which includes broader restrictions on the use of gun trace data.