Attorney General Alberto Gonzales said this afternoon that he was disappointed with the decision, and that while the stay is in place “we will continue to utilize the program to ensure that America is safer.” Mr. Gonzales said he remained confident that the program was constitutional, and that Congress had given the president all the authority he needed when it authorized the use of military force after the Sept. 11 attacks.

Earlier, the Justice Department called the surveillance program “a critical tool” against Al Qaeda and said the parties to the suit have agreed to a stay of Judge Taylor’s order until the Sept. 7 hearing. On that day, the judge will be asked to prolong the stay of her order pending further appeals, to the Court of Appeals for the Sixth Circuit or perhaps to the Supreme Court.

Some Republicans voiced disappointment over the ruling, while Democrats praised it. The starkly different reactions signaled more heated debate on Capitol Hill when Congress reconvenes.

But for the moment, the ruling by Judge Taylor caused elation among the plaintiffs.

“It’s another nail in the coffin of executive unilateralism,” said Jameel Jaffer, a lawyer for the plaintiffs with the A.C.L.U. And Anthony Romero, executive director of the A.C.L.U., said Judge Taylor’s ruling “confirms that the government has been acting illegally, in contravention of the Foreign Intelligence Surveillance Act and the Fourth Amendment.’’

The surveillance act was passed by Congress in 1978 in response to disclosures of previous government improprieties in eavesdropping. The act established a secret court to handle applications for surveillance operations, and set up procedures for them to take place while applications for warrants are pending in some limited circumstances and for limited times.

Judge Taylor said “the president has acted, undisputedly, as F.I.S.A. forbids,” thus defying the express will of Congress, and she was unpersuaded by the government’s stance that it could not defend itself in the lawsuit without doing the country harm.