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“The airports are on city property,” he said. He said the city could not ban screening, but did have the jurisdiction to forbid the use of the AIT machines within its borders.

A City Council official, who would speak only on the condition of anonymity, told The Times that council staff members were reviewing Mr. Greenfield’s legislative proposal and would consider “a range of issues,” including whether the City Council had jurisdiction, before making a decision about whether to move a bill forward.

Mr. Greenfield said he and other council members also were encouraging the Port Authority of New York and New Jersey, which runs the two New York airports and Newark Liberty International Airport in New Jersey, to opt out of the TSA system.

Under the federal legislation that set up the agency, airports across the country can have federally certified private firms handle their passenger and baggage screening under TSA supervision — employing the same technology and procedures that the agency does. Seventeen airports across the country have opted out. They range in size from one major international hub — San Francisco — to a series of much smaller airports such as Jackson Hole Airport in Wyoming.

“We are encouraging them to look at the opt-out,” said Mr. Greenfield, of the Port Authority, adding that officials there were “considering it.” He said he hoped to start a grass-roots movement that would force federal authorities to reconsider their use of the machines.

“If other cities legislate … maybe they will have to listen,” he said.

A Port Authority spokesman referred queries to the TSA, which did not respond to a request for comment. But a senior Department of Homeland Security official authorized to talk to the media only on background told The Times that the federal law that gave TSA the right to regulate aviation security “would supercede any state or local ordinance.”

“All commercial airports are regulated by TSA, whether the actual screening is performed by TSA or private companies. So TSA’s policies — including advanced-imaging technology and pat-downs — are in place at all domestic airports,” the agency says on its website.

Nonetheless, other airports around the country are exploring the opt-out alternative.

Florida’s Mr. Dale said that, unlike the federal government, private companies “have to get [their revenue] the old-fashioned way, they have to earn it every day.”

He acknowledged that the screeners still would have to carry out TSA procedures as mandated, but added that he thought the measures were unconstitutional. “As a law enforcement officer, you can’t search people the way they do with these pat-downs without probable cause,” he said. “It is an unreasonable search.”

While standing by the policy, Mr. Pistole hinted to reporters that he regretted having rejected the advice of his media advisers to make the measures public before they were introduced.

“I wish I could say somebody else was responsible for that, but that was my decision,” he said.

“Rather than publicize the fact that we were doing this, I made an intentional decision that we would not do that. We would roll it out … and then try to educate the public once we did that,” he said. “My concern was … [advance notice] would then provide a road map or a blueprint to a putative terrorist.”