Washington ? Membership in the American Civil Liberties Union and similar groups has soared since the Sept. 11, 2001, terrorist attacks, an increase that is especially noteworthy because the ACLU appears to be making significant headway among conservatives, who have traditionally despised the organization.

The ACLU has signed up such prominent conservatives as former Rep. Bob Barr, R-Ga., a firebrand whom liberals loved to hate when he was in Congress. It has formed lobbying alliances with right-leaning groups from the American Conservative Union to Americans for Tax Reform.

“You name it, we’ve gone into bed with them,” said ACLU spokeswoman Emily Whitfield.

While it is impossible to know for sure, ACLU leaders and conservatives believe a major portion of the 100,000 members who have joined since the Sept. 11 attacks have come from conservative ranks. The dramatic expansion has brought the ACLU’s membership to 400,000, by far the largest in the group’s 80-year history.

The increase suggests that despite the war on terrorism, many Americans remain deeply troubled by the potential for the federal government overreaching that is embodied in such antiterrorism measures as the USA PATRIOT Act, which expands eavesdropping powers. The ACLU has often served as a barometer of public anxiety about big government.

The ACLU’s expansion is not unique; the Electronic Frontier Foundation, which focuses on Internet privacy, has nearly doubled from 5,000 members to 9,000. “It’s a general sense of fear and distrust of government, and concern that police and the Department of Justice are getting more power than they should have,” said Kevin McLaughlin, the foundation’s membership director.

But it is the ACLU, the nation’s premier civil liberties group, that has undergone the most striking transformation. The group, which has always claimed to be nonpartisan, is seizing on the attacks in an attempt to remake itself — polishing its image, aggressively reaching out to conservatives and launching new ads.

“I think the ACLU is taking its reputation and its image more seriously,” said Laura Murphy, who heads the group’s Washington office. “What we are doing … is repositioning the ACLU. And for some people, they’re rediscovering us on a whole panoply of issues.”

That is especially true of conservatives, who previously had little time for the ACLU but are deeply concerned about the Bush administration’s antiterror initiatives. “It’s scared a lot of conservatives,” Barr said. “They now recognize that we do have common ground with the ACLU.”