DETROIT (Reuters) - The American Civil Liberties Union filed a lawsuit against the federal government on Wednesday aimed at curbing the vastly expanded spy powers won under the anti-terrorism law passed soon after the Sept. 11 attacks

The suit, filed in federal court in Detroit on behalf of six Arab-American groups, targets a key provision of the USA Patriot Act that gives the FBI more leeway to conduct domestic surveillance.

``This lawsuit is the first legal challenge to the USA Patriot Act, passed shortly and with almost no public debate after the terrorist attacks of September 11th,'' said Kary Moss, director of the Michigan chapter of the ACLU.

``The Ashcroft administration has launched a war on all of us by strategically trying to cut back the protections of the Bill of Rights,'' she said at a news conference.

Attorney General John Ashcroft, who has described the Patriot Act as a critical weapon in the war declared by President Bush after the attacks on the Pentagon and World Trade Center, is a defendant in the ACLU suit along with FBI Director Robert Mueller.

Under Section 215 of the Patriot Act, which the lawsuit challenges as unconstitutional, the FBI can secretly search and seize records, books, papers or other personal belongings of practically anyone, without a warrant and without showing probable cause.

The agency can also impose a lifelong ``gag'' order prohibiting anyone served with Section 215 orders -- aimed for example at getting information about a suspect's medical history, reading habits, political activities or religious affiliation -- from telling someone else about the investigation.

SECTION 215 DEFENDED

A Justice Department spokesman in Washington said it would have no immediate comment about the ACLU's lawsuit. But the department later issued a statement defending Section 215, saying it could only be used to conduct a narrow set of investigations.

``It should be noted that criticism of Section 215 frequently ignores what the provision actually includes,'' said Justice Department spokeswoman Barbara Comstock.

The ACLU's lawsuit was filed just a week after the Republican-controlled U.S. House of Representatives voted overwhelmingly to roll back another key provision of the Patriot Act. And Moss said more than 143 cities across the nation have now passed local resolutions against the Patriot Act in what she described as a groundswell of opposition to ``the government's war on the Bill of Rights.''

Mary Rose Oakar, head of the Arab-American Anti-Discrimination Committee that is one of the six plaintiffs in the ACLU case, noted that Arabs and Muslim-Americans have been the primary target of the FBI's counter-terror measures after Sept. 11.

But at the news conference at the ACLU's headquarters in Detroit, which is home to a large Arab-American community, Oakar said the ``chilling effects of the Patriot Act could happen to anyone'' and warned against the erosion of U.S. civil liberties.

``This is an un-American, unconstitutional act. It must be challenged to protect the basic rights of the people of the United States of America,'' she said.