DETROIT – A federal judge ruled Thursday that the government’s warrantless surveillance program is unconstitutional and ordered an immediate end to it.

U.S. District Judge Anna Diggs Taylor in Detroit became the first judge to strike down the National Security Agency’s program, which she says violates the rights to free speech and privacy, as well as the separation of powers enshrined in the Constitution.

“Plaintiffs have prevailed, and the public interest is clear, in this matter. It is the upholding of our Constitution,” Taylor wrote in her 43-page opinion.

The Justice Department said it is appealing the ruling.

“We’re going to do everything we can do in the courts to allow this program to continue,” Attorney General Alberto Gonzales said at a news conference in Washington.

Gonzales maintained that the program is legal and useful.

“”We’ve had numerous statements by leaders of the intelligence community about the effectiveness of the program in protecting America,” he said.

White House press secretary Tony Snow said the Bush administration “couldn’t disagree more with this ruling.”

“The program is carefully administered and only targets international phone calls coming into or out of the United States where one of the parties on the call is a suspected al-Qaida or affiliated terrorist,” Snow said.

The ruling won’t take immediate effect, so Taylor can hear a Justice request for a stay pending its appeal. A hearing on the motion was set for Sept. 7, Snow said.

The American Civil Liberties Union filed the lawsuit on behalf of journalists, scholars and lawyers who say the program has made it difficult for them to do their jobs.

The union believes that many of their overseas contacts are likely targets of the program, monitoring phone calls and e-mails between people in the U.S. and people in other countries when a link to terrorism is suspected.

The government argued that the program is well within the president’s authority, but said proving that would require revealing state secrets.

The ACLU said the state-secrets argument was irrelevant because the Bush administration already had publicly revealed enough information about the program for Taylor to rule.

“At its core, today’s ruling addresses the abuse of presidential power and reaffirms the system of checks and balances that’s necessary to our democracy,” ACLU executive director Anthony Romero told reporters after the ruling.

He called the opinion “another nail in the coffin in the Bush administration’s legal strategy in the war on terror.”

While siding with the ACLU on the surveillance issue, Taylor dismissed a separate claim by the group over NSA data-mining of phone records.

Traulor said that not enough had been publicly revealed about that program to support the claim and added that further litigation against the program would jeopardize state secrets.

The lawsuit alleged that the NSA “uses artificial intelligence aids to search for keywords and analyze patterns in millions of communications at any given time.”

Lawsuits have been filed over data-mining against phone companies, accusing them of improperly turning over records to the NSA.

However, the data-mining was only a small part of the Detroit suit, said Ann Beeson, the ACLU’s associate legal director and the lead attorney on the case.

Beeson predicted the government would appeal the wiretapping ruling and request that the order to halt the program be postponed while the case makes its way through the system.

Beeson said the ACLU had not yet decided whether it would oppose such a postponement.