The White House issued a strong-worded statement on Thursday, defending the warrantless eavesdropping program as "firmly grounded in law," hours after a federal judge ruled the program unconstitutional and ordered its immediate halt.

"We couldn't disagree more with this ruling, and the Justice Department will seek an immediate stay of the opinion and appeal," the statement said.

Earlier Thursday, US District Judge Anna Diggs Taylor ruled in Detroit, Michigan, that the Bush administration's warrantless eavesdropping program run by the National Security Agency (NSA) was unconstitutional.

Taylor, the first judge to rule against the program since its disclosure last December, said the program violated the separation of powers doctrine, the Administrative Procedures Act, the constitution, and the law governing domestic wiretapping.

In its statement, the White House said the program was "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."

The whole point of the program, the statement said, was to "detect and prevent terrorist attacks before they can be carried out" and that it was the president "most solemn duty to ensure their protection."

Describing the program as "one of our most critical and effective tools in the war against terrorism," the statement said the parties concerned had agreed that enforcement of the ruling would be stayed, until the court would conduct a hearing scheduled for Sept. 7 on the ruling.

The Justice Department, calling the program "a critical tool" to detect and prevent a terrorist attacks in the anti-terrorism war, said it would appeal the ruling.

In a statement, the department said the president had the primary duty under the constitution to protect the American people, and that the constitution gave the president the "full authority necessary to carry out that solemn duty, and we believe the program is lawful and protects civil liberties."

The lawsuit was filed in January by the American Civil Liberties Union, on behalf of some journalists, scholars and lawyers who said many of their overseas contacts might be targeted by the program and that made their work difficult.

Shortly after the program's disclosure, Bush acknowledged that he had authorized the NSA to eavesdrop, without court warrants, on international calls and international e-mails of people suspected of having links to terrorists when one party to the communication was in the United States.

A law, the 1978 Foreign Intelligence Surveillance Act, makes it illegal to spy on US citizens in the United States without warrants issued by a secret court.

The revelation of the program created a political debate in Washington, and congressional hearings have been held to investigate its legality.

(Xinhua News Agency August 18, 2006)