A grassroots movement to have municipal governments crack down on illegal immigrants is reeling after a federal judge declared unconstitutional a Pennsylvania city’s attempt to deny housing and jobs to foreigners who lack permission to live in America.

In a legal case watched closely by both sides in the immigration debate, Judge James Munley ruled yesterday that ordinances passed in Hazleton, Pa., usurped the federal government’s right to set immigration policy.

“This decision is a historic decision as it delivers a body blow to this effort by localities to try to regulate immigration,” one of the lawyers fighting the ordinances, Foster Maer of the Puerto Rican Legal Defense and Education Fund, said.

In a 206-page opinion, Judge Munley identified what he found to be a host of legal problems with the Hazleton ordinances, which were passed last year based on contentions that illegal immigrants were committing crimes and living in unsanitary, overcrowded conditions.

One of the two disputed ordinances required employers to give the city records verifying the legal immigration status of all employees and subjected landlords to penalties for harboring illegal immigrants. The other rules set up a residency permit scheme under which Hazleton apartment dwellers would have to provide proof of the right to live in America.

“Immigration is a national issue,” Judge Munley declared. “Whatever frustrations officials of the city of Hazleton may feel about the current state of federal immigration enforcement, the nature of the political system in the United States prohibits the city from enacting ordinances that disrupt a carefully drawn federal statutory scheme.”

Proponents of the ordinances said they were legitimate because only illegal immigrants would be inconvenienced by them, but Judge Munley rejected that argument out of hand. “We cannot say clearly enough that persons who enter this country without legal authorization are not stripped immediately of all their rights because of this single illegal act,” the judge wrote. “The contemporary concern with and opprobrium towards undocumented aliens does not lead us to the conclusion that those who violate the laws to enter the United States can be subject without protest to any procedure or legislation, no matter how violative of the right to which those persons would normally be entitled.”

The mayor of Hazleton, Louis Barletta, predicted an appeal. “This small city is not willing to stop fighting yet,” he told CNN. Mr. Barletta also expressed exasperation at federal authorities for not getting a grip on immigration. “If they were doing their job, obviously I wouldn’t have to take this stand,” he said.

A candidate for the Democratic presidential nomination, Senator Obama of Illinois, issued a statement last night hailing the judge’s ruling as “a victory for all Americans.” “The anti-immigrant law passed by Mayor Barletta was unconstitutional and unworkable — and it underscores the need for comprehensive immigration reform so local communities do not continue to take matters into their own hands,” Mr. Obama said.

A law professor who supported the city, Jan Ting of Temple University, voiced disappointment at the ruling. “I did think that the statute was carefully crafted to respect federal immigration law,” he said.

A federal law passed in 1986 bars states from imposing civil and criminal sanctions in connection with the employment of illegal immigrants. However, the federal statute allows states to pursue “licensing and similar laws” that touch on the issue. For that reason, Hazleton structured its ordinances as licensing requirements, but Judge Munley said they still intruded on federal turf.

Immigrant rights advocates said they hoped the court victory would discourage other cities and towns from passing ordinances aimed at illegal immigrants. “Many local officials are, frankly, being duped into adopting bad public policies,” the executive director of the American Civil Liberties Union, Anthony Romero, said.

While the term “illegal alien” is widely bandied about, Judge Munley wrote that determining the legal status of a specific individual can be difficult. Federal immigration law allows for a variety of grounds to forestall deportation or removal. Many of these individuals could still be considered illegal aliens, even though the government cannot throw them out or has chosen not to. “Although these aliens are permitted to work and implicitly to remain in the United States, they would be denied housing in Hazleton,” the judge said.

Judge Munley, who was appointed by President Clinton, also expressed concern that the ordinances would have a particular impact on “those who look or act as if they are foreign.”

An advocate of tighter immigration controls, Ira Mehlman of the Federation for American Immigration Reform, said federal immigration law does contemplate the involvement of local authorities in enforcement and instructs the federal government to verify the legal status of persons suspected to be illegal immigrants by municipalities.

Mr. Mehlman said pro-immigrant forces are selective about when they want local officials to butt out on the issue. He noted that New Haven, Conn., recently agreed to give city-issued identification to illegal immigrants. “We can expect the ACLU to take New Haven to court now?” he asked rhetorically. “I’m not holding my breath.”