Washington ? Atty. Gen. John Ashcroft defended the Patriot Act on Tuesday, saying the anti-terrorism measure passed by Congress after the Sept. 11 attacks has been key to the nation’s efforts to thwart attacks against Americans.

In a speech to the conservative-leaning think tank American Enterprise Institute, Ashcroft sought to counter critics who say the act gives law enforcement unnecessary and overreaching powers that threaten the privacy rights of innocent people.

Ashcroft said the law has given police and prosecutors the tools needed to thwart would-be terrorists within the parameters of the Constitution. He gave several examples where the act allowed law enforcement officials to bring charges against suspects thought to be plotting attacks or supporting terror groups.

“If we knew then what we know now, we would have passed the Patriot Act six months before Sept. 11 rather than six weeks after the attacks,” he said. ” … The cause we have chosen is just. The course we have chosen is constitutional.”

Ashcroft cited elements of the law that he says make it easier for law enforcement officials to pursue suspected criminals. For example, prosecutors no longer must get permission for different wiretaps every time a suspect changes cell phones. Instead, the wiretap provision applies to the suspect rather than a specific phone.

Ashcroft’s speech marked the start of a campaign-style offensive aimed at countering criticism from leading Democrats and civil liberties advocates about the Patriot Act.

He plans a road trip today and Thursday, with remarks to law enforcement audiences in Philadelphia, Cleveland, Detroit and Des Moines, Iowa.

Among the dozen or so future stops are Salt Lake City and Boston, officials said. The Justice Department put up an Internet site to reinforce the pro-Patriot Act message and all 94 U.S. attorneys are being encouraged to hold town hall-style meetings to stress the law’s benefits in fighting terrorism.

“There is a lot of confusion about what the Patriot Act does and does not do,” said Mary Beth Buchanan, U.S. attorney in Pittsburgh. “We are going to try to better educate the public.”