A prominent U.S. civil liberties organization Tuesday announced it filed a lawsuit in Detroit challenging the legality of the National Security Agency's warrantless surveillance program. President Bush's decision to use the NSA to monitor some communications between U.S. citizens and terror suspects abroad has been the subject of an often heated debate in Congress and the media.

The American Civil Liberties Union told reporters its case is the first legal challenge to the Bush administration's wiretapping program. The ACLU has filed the lawsuit on behalf of a group of scholars, journalists and attorneys who argue the governmen's eavesdropping program is interfering with their ability to keep their communications private.

The ACLU's associate legal director, Ann Beeson, said the government has already admitted some key points in the litigation. "The government has already conceded that they are wiretapping Americans without a warrant and that they are not complying with procedures that Congress legislated through the Foreign Intelligence Surveillance Act," she said.

But the government has asked that the Detroit court to dismiss the case on the grounds it could compromise state secrets.

The domestic eavesdropping program bypasses a 1978 law that requires the U.S. government to get a warrant from a special surveillance court before it starts to monitor phone calls and other communications involving U.S. citizens or legal residents.

President Bush has repeatedly defended his decision, made after the September 11, 2001, terrorist attacks, to authorize the secret surveillance progam, saying it is both legal and an essential tool in the war on terror: "Americans expect their government to do everything in its power under our laws and Constitution to protect them and their civil liberties. That is exactly what we are doing. And so far, we have been successful in preventing another attack on our soil," he said.

But critics and some opposition Democratic lawmakers have questioned the legality of the NSA program, calling it an abuse of presidential power and an infringement of Americans' basic right to privacy.

A court hearing in the case will be held June 12.