A memorandum from two congressional legal analysts concludes that the administration's justification for the monitoring of certain domestic communications may not be as solid as President Bush and his top aides have argued.

The Congressional Research Service, which advises lawmakers on a wide range of matters, said a final determination about the issue is impossible without a deeper understanding of the program and Bush's authorization, "which are for the most part classified."

Yet two attorneys in the organization's legislative law division, Elizabeth Bazan and Jennifer Elsea, say the justification that the Justice Department laid out in a Dec. 22 analysis for the House and Senate intelligence committees "does not seem to be as well-grounded as the tenor of that letter suggests."

The National Security Agency 's activity "may present an exercise of presidential power at its lowest ebb," Bazan and Elsea write in the 44-page memo.

Bush and his top advisers have defended the program, which allowed the highly secretive agency to eavesdrop without court approval on international calls and e-mails of people who were inside the United States and suspected of communicating with Al Qaeda or its affiliates.

The Bush administration says it was legal under Article 2 of the Constitution, which grants presidential powers, and Congress' September 2001 authorization to use military force to conduct the War on Terror.

But the memo concludes: "It appears unlikely that a court would hold that Congress has ... authorized the NSA electronic surveillance operations here under discussion."

Responding to the report, Justice Department spokesman Brian Roehrkasse said the activities "were conducted in accordance with the law and provide a critical tool in the war on terror that saves lives and protects civil liberties."

The domestic monitoring has raised questions about the appropriate powers of Congress and the executive branch. Congress' legal advisers are saying lawmakers should have a role in overseeing such activities.

Ken Bass, a Carter administration Justice Department official and an expert on the Foreign Intelligence Surveillance Act, said the issue of the president's inherent power has remained unresolved for decades.

The White House's analysis of presidential power is consistent with previous administrations, Bass said. But he said he didn't know of an administration that had asserted authority for four years, as in the monitoring program, to delegate decisions normally requiring court orders to midlevel intelligence officials.

On Monday, Bush reasserted his authority to order the surveillance.

"The enemy is calling somebody, and we want to know who they're calling and why," Bush said in San Antonio, Texas. "And that seems to make sense to me, as the commander in chief, if my job is to protect the American people."

Sen. Frank Lautenberg, D-N.J., who was among those who requested the research service's memo, said it contradicts Bush's claim that the program was legal.

"It looks like the president's wiretapping was not only illegal, but likely targeted innocent Americans who did nothing more than place a phone call," he said.