The White House on Tuesday threatened a veto of the fiscal 2009 defense authorization bill that the Senate was expected to take up later in the day.

The provisions drawing the veto threat included three sections of the bill to restrict the Pentagon’s ability to hire private contractors and limit their role in the war, plus a possible amendment requiring congressional approval of a U.S.-Iraq security pact that is now under negotiation.

The Senate was to take up the bill if Republicans and Democrats can agree on a list of allowable amendments first circulated Monday. Democratic leaders hope to pass the bill by week’s end, though key senators say meeting that schedule will be a challenge.

The measure would authorize $612.5 billion in national security programs at the Defense and Energy departments in fiscal 2009, which begins Oct. 1. Included in that sum is $70 billion for operations in Iraq and Afghanistan and a pay raise for U.S. troops. The House passed its own version of the measure in May.

The White House, in a statement of administration policy, threatened a veto if the bill retains one provision that would severely restrict the use of contractors as security guards in combat zones, or a second barring use of contractors to interrogate detainees, or a third that would ban under certain circumstances public-private competitions for Defense Department work. All three provisions exist in identical or similar form in the House-passed version as well.

The administration also threatened to veto the bill over a variety of stipulations on how the Defense Department should organize personnel in its intelligence agencies.