WASHINGTON -- The new chairman of the House Judiciary Committee, John Conyers Jr. of Michigan, said yesterday that he is launching an aggressive investigation into whether the Bush administration has violated any of the laws it claimed a right to ignore in presidential "signing statements."

Bush has claimed that his executive powers allow him to bypass more than 1,100 laws enacted since he took office. But administration officials insist that Bush's signing statements merely question the laws' constitutionality, and do not necessarily mean that the president also authorized his subordinates to violate them.

Conyers said the president has no power " to ignore duly enacted laws he has negotiated with Congress and signed." And he vowed to find out whether the administration has followed each law it challenged -- including laws touching on classified national security matters, such as the tactics used to interrogate suspected terrorists and the FBI's use of the Patriot Act.

"This is a constitutional issue that no self-respecting federal legislature should tolerate," Conyers said, and he added that the committee was determined to "get to the bottom of this matter, and to be blunt, we are not going to take no for an answer."

The Michigan Democrat made his remarks at the committee's first oversight hearing since Democrats took control of Congress, which Conyers devoted to signing statements. He called the hearing a kickoff to his plans to use the coming session to probe the administration's "growing abuse of power."

Democrats on the Judiciary Committee are beefing up their staff by hiring a special "oversight and investigative unit" of about six attorneys to lead the panel's probes of the administration. The group is headed by Elliot Minc- berg , formerly the general counsel of the liberal activist group People for the American Way.

Republicans on the committee complained about the hearing, saying that the controversy over the Bush administration's signing statements is overblown.

But Democrats said they wanted to know whether Bush has followed through on his claims that the Constitution gives him the power to exempt executive branch officials from laws that Congress has passed to regulate the government, including affirmative action hiring requirements, a ban on all forms of torture, and oversight provisions in the Patriot Act.

Deputy Assistant Attorney General John P. Elwood testified that the committee will find nothing amiss. He noted that Bush has repeatedly said his administration does not torture, and said that the Department of Justice has not held back any information from Congress about its use of the Patriot Act.

Elwood also rejected the notion that Bush's signing statements represent a "power grab." Whatever power the Constitution gives the president, he said, exists regardless of the president's decision to note it in a signing statement. "Congress has no power to enact unconstitutional laws . . . whether the president issues a signing statement or not," Elwood said, adding Bush has attached signing statements to about the same number of bills as his recent predecessors of both parties.

But critics said that it is misleading to focus on the number of bills instead of the number of challenges, since Congress often lumps many different laws together in a single omnibus bill.

Bush has used signing statements to challenge 1,149 laws that were contained in 150 bills, according to data compiled by Christopher Kelley, a political science professor at Miami University in Ohio . By comparison, all previous presidents combined challenged about 600 total laws.

The American Bar Association last year sounded an alarm about the escalating use of signing statements. ABA president Karen Mathis testified that it is "contrary to the rule of law and our constitutional system of separation of powers" for a president to sign a bill and then instruct the executive branch that parts are unconstitutional. Presidents must either veto a bill and give Congress a chance to override their judgments, or they must sign it and obey all of it as written, she said.

Harvard Law School professor Charles Ogletree testified that signing statements create potential dangers even if the executive branch does not violate the laws.

Ogletree cited a signing statement Bush attached to a December 2006 law banning the transfer of nuclear technology to India if it violates international non proliferation guidelines. Bush claimed that he has independent power to run America's foreign affairs and so he would view the ban as merely "advisory."