NEW YORK (Reuters) - A nationwide tour by America's top prosecutor to promote a hotly debated counterterrorism law ended on Tuesday in New York as it began -- with applause at a closed-door meeting and a raucous protest outside.

Attorney General John Ashcroft spoke in New York two days before the second anniversary of the Sept. 11 attacks on the United States that spurred the sweeping legislation known as the Patriot Act.

The act passed by Congress in Oct. 2001 is the centerpiece of President Bush's campaign to fight terrorism on U.S. soil. But the law has been criticized by both liberals and conservatives who say it violates the constitution, allowing the government to abuse its ability to conduct surveillance and keep secret some search warrants.

Ashcroft's appearance so close to the emotional anniversary at Federal Hall in the Wall Street neighborhood just blocks from the destroyed World Trade Center, angered civil liberties groups who gathered about 1,500 demonstrators as he spoke.

Ashcroft, in a prepared speech to an invited audience of mostly law enforcement officials, defended the legislation as a valuable anti-terrorism tool.

"We have used tools provided in the Patriot Act to fulfill our first responsibility -- that of protecting the American people," said Ashcroft, whose 16-city tour has been likened by the media to an election campaign. "We've used these tools to provide the security that ensures liberty."

The U.S. Justice Department has gradually released Ashcroft's tour schedule, but a Washington official said they were not aware of any further stops being announced.

Outside on the street, New York Civil Liberties Union executive director Donna Lieberman reminded the crowd how the Sept. 11 attacks shook the city of 8 million people and that security is of greater concern than ever before.

"Of course we want to be safe, but the government of the United States under the leadership of George Bush and John Ashcroft has perpetrated a cruel hoax on the American people," Lieberman said. "It has taken advantage of this unspeakable tragedy to launch a broadside against our fundamental rights."

Protesters chanted "Hey Ashcroft, you leave our Bill of Rights alone" and "Ashcroft Go Home" and held up signs such as "Dissent is Patriotic."

The protest was co-sponsored by the NYCLU and the New York Bill of Rights Defense Campaign.