The ABA group, which includes a one-time FBI director and former federal appeals court judge, said the president has overstepped his authority in attaching challenges to hundreds of new laws.
The attachments, known as bill-signing statements, say Mr. Bush reserves a right to revise, interpret or disregard measures on national security and constitutional grounds.
"This report raises serious concerns crucial to the survival of our democracy," said the ABA's president, Michael Greco. "If left unchecked, the president's practice does grave harm to the separation of powers doctrine, and the system of checks and balances that have sustained our democracy for more than two centuries."
Some congressional leaders had questioned the practice. The task force's recommendations, being released today in Washington, will be presented to the 410,000-member group next month at its annual meeting in Hawaii.
ABA policymakers will decide whether to denounce the statements and encourage a legal fight over them.
The task force said the statements suggest the president will decline to enforce some laws. Bush has had more than 800 signing statement challenges, compared with about 600 signing statements combined for all other presidents, the group said.
Noel J. Francisco, a former Bush administration attorney who practices law in Washington, said the president is doing nothing unusual or inappropriate.
"Presidents have always issued signing statements," he said. "This administration believes that it should make clear ... when the Congress is getting close to the lines that our Constitution draws."
Francisco said the administration's input is part of the give and take between the branches of government. "I think it's good that the debate is taking place at a public level," he added.
White House Press Secretary Tony Snow said last month that "it's important for the president at least to express reservations about the constitutionality of certain provisions."
The ABA report said President Reagan was the first to use the statements as a strategic weapon, and that it was encouraged by then-administration lawyer Samuel Alito — now the newest Supreme Court justice.
The task force included former prosecutor Neal Sonnett of Miami; former FBI Director William Sessions; Patricia Wald, former chief judge of the U.S. Court of Appeals for the District of Columbia Circuit; former Republican Rep. Mickey Edwards; and former Reagan administration lawyer Bruce Fein; and law school professors and other lawyers.