WASHINGTON, July 2, 2005 (Reuters) - The White House on Thursday threatened to veto a massive Senate bill for $442 billion in next year's defense programs if it moves to regulate the Pentagon's treatment of detainees or sets up a commission to investigate operations at Guantanamo Bay prison and elsewhere.

The Bush administration, under fire for the indefinite detention of enemy combatants at Guantanamo Bay in Cuba and questions over whether its policies led to horrendous abuses at Abu Ghraib prison in Iraq, put lawmakers on notice it did not want them legislating on the matter.

In a statement, the White House said such amendments would "interfere with the protection of Americans from terrorism by diverting resources from the war."

"If legislation is presented that would restrict the president's authority to protect Americans effectively from terrorist attack and bring terrorists to justice," the bill could be vetoed, the statement said.

Republicans on the Senate Armed Services Committee were considering a range of amendments intended to prevent further abuses in the wake of the scandal over sexual abuse and mistreatment of prisoners at Abu Ghraib prison and harsh, degrading interrogations at Guantanamo.

Sen. John McCain of Arizona, on his way to a meeting on the defense bill with Vice President Dick Cheney at the Capitol, said he would "listen to their arguments" before deciding whether to go ahead with detainee amendments.

"We've had discussions with them. I hope to continue to have discussions with them," said McCain, who endured torture as a prisoner of war in Vietnam.

McCain, along with Armed Services Committee Chairman John Warner of Virginia and Lindsey Graham of South Carolina, were considering several amendments.

Under discussion were measures defining the legal status of enemy combatants at Guantanamo, barring the holding of "ghost" detainees whose names are not disclosed, codifying a ban against cruel, inhumane or degrading treatment, and using the Army manual as a basis for all interrogations.

Democrats on Thursday said they would push an amendment to establish an independent national commission to investigate policies that led to abuses of prisoners at Abu Ghraib, Guantanamo Bay which mostly holds prisoners picked up from the U.S.-led offensive in Afghanistan, and elsewhere.

Sen. Carl Levin of Michigan, the Armed Services Committee's top Democrat, said the commission on detainee abuses was needed because "the most serious scandal in recent military history needs an objective investigation."

Levin said the commission should be modeled on the bipartisan commission that probed the Sept. 11, 2001, attacks.

Sen. Edward Kennedy of Massachusetts said the Pentagon's own investigations into detainee abuses left "huge gaps ... The military reviewing itself, that's not good enough."