WASHINGTON — The US Senate on Wednesday will take up its annual Pentagon policy bill, but senior Democrats are doubling down on a White House veto threat.

The legislation, overwhelmingly approved recently by the Senate Armed Services Committee, would authorize nearly $590 billion in 2016 base defense and war spending. But it contains a slew of proposals opposed by Democrats and the White House.

Atop that list is an $88 billion overseas contingency operations (OCO) account, grudgingly included by SASC Chairman John McCain, R-Ariz., after GOP leaders concluded the lone way to keep their defense hawks happy was to give the Pentagon more cash via the off-budget war account.

Senate Minority Leader Harry Reid, D-Nev., told reporters Tuesday the White House is serious about President Barack Obama's promises on federal spending.

"The president said he's going to veto it, so I think it really is kind of a waste of time," Reid said of Majority Leader Mitch McConnell's decision to bring up the bill. "But that's the way it is. We wasted a lot of time here in recent months."

On Wednesday morning, McConnell urged Democrats to support the defense bill.

"Blocking this bill is not in our national interest," he said. "So let's skip the partisan games and start working toward common-sense reforms, as this bill proposes."

Just how the floor proceedings play out remains murky. Democrats, like Obama, view swelling the Pentagon war fund with monies that will be used for things typically funded in the base budget as an unwise "gimmick." And they want GOP members to agree to domestic spending hikes in return for the extra defense dollars.

"We'll see what happens," Reid said cryptically.

On Tuesday evening, the White House issued a statement of administration policy detailing its gripes with the legislation. Along with the inflated OCO account, the legislation resists the administration's desired base-closure round and numerous weapon program proposals.

Unless many of those SASC moves are reversed on the floor, the White House policy document states, "the president's senior advisors would recommend to the president that he veto it."

"The president has been very clear about the core principle that he will not support a budget that locks in [budget caps], and he will not fix defense without fixing non-defense spending," according to the White House statement. "Unfortunately, the bill fails to authorize sufficient funding for our military's priorities in the base budget, and instead uses overseas contingency operations (OCO) funding in ways that leaders of both parties have made clear are inappropriate.

"Shifting base budget resources into OCO risks undermining a mechanism meant to fund incremental costs of overseas conflicts and fails to provide a stable, multi-year budget on which defense planning is based," the White House said. "The use of OCO funding to circumvent budget caps in defense spending also ignores the long-term connection between national security and economic security and fails to account for vital national security functions carried out at non-defense agencies."

Some good-government groups, budget analysts and an increasing number of lawmakers in both parties see the account as a "slush fund," saying the Pentagon should be able to account for war costs within its base budget after nearly 14 years of conflict with radical Islamic groups.

Defense sector sources doubt Obama would veto a bill containing so many policy provisions that would affect US troops. But congressional aides have acknowledged one reason the Senate is taking up the bill earlier than in recent years is in case he does just that, giving lawmakers and aides time to try again.

The legislation also contains McCain's sweeping proposed overhaul of the Pentagon acquisition system. His idea is to make the armed service chiefs more involved in managing their major weapon programs, and thereby, more accountable. But McCain's language also seems to erode the authorities of the Pentagon acquisition chief.

The White House opposes McCain's defense acquisition reform proposals., calling tThe bill's language is "inconsistent with the secretary of defense's exercise of authority, direction and control over all of the DoD programs and activities."

"Since DoD's founding, the secretary of defense has served as the principal assistant to the president in all matters relating to DoD and subordinated the departments of the Army, Navy and Air Force to the secretary's authority," the White House said. "This provision would undermine this principle by seeking to exclude the [defense] secretary and his assistants from certain matters entrusted exclusively to the military departments."

The administration also claims one part of McCain's plan "would significantly reduce the secretary of defense's ability — through the undersecretary of defense for acquisition, technology and logistics USD (AT&L) — to guard against unwarranted optimism in program planning and budget formulation, and prevent excessive risk taking during execution — all of which is essential to avoiding overruns and costly delays."

The Senate is slated to begin debating the bill at 11 a.m. Wednesday. At time of publication, no amendment votes were expected Wednesday. Final passage could occur next week.

Twitter: @bennettjohnt