In a briefing at the Pentagon, Secretary Gates will address the current (and yet to be approved) 2011 Defense Department budget, where he's expected to announce a number that he can "live with", a senior defense official tells FOX News.

The number is expected to be a compromise between the $529 billion the Pentagon is now operating under as part of a continuing resolution, and the $549 billion base budget it requested for FY 2011.

He'll also reinforce proposed cuts for the FY 2012 budget, which he first announced on January 6th of this year.

Here's a little history of defense spending these past years under President Obama:

-In 2010 there was a base budget of $531 billion, with an additional $130 billion to fund the wars in Iraq and Afghanistan, known as OCO (Overseas Contingency Operations) funding. President Bush called it Global War on Terror or GWOT funding, a term dropped by Obama. Later in 2010 President Obama added another $33 billion in supplemental spending to fund the 30,000-man troop surge in Afghanistan.

2010 grand total: $694,000,000,000

-The proposal for FY 2011 asked for a $549 billion base, with $159 in OCO spending.

2011 proposed grand total: $708,000,000,000

-The FY 2012 defense budget asks for $553 billion in base spending, with $118 billion for the wars. That significant decrease in war spending is directly related to heavy troop withdrawals in Iraq.

2012 proposed grand total: $671,000,000,000

Although the grand total is less in 2012 than it is in 2011, the base budget request is up slightly. That increase, Pentagon officials say, accounts for inflation only.

In January Secretary Gates announced a plan to cut $78 billion in defense spending over five years. The largest savings would come from shrinking the size of the Army by 27,000 soldiers and the Marines by 15 - 20,000 in the year 2015. That assumes the war in Afghanistan will be over for the U.S. by the end of 2014.

Gates also proposed $7 billion in savings by increasing premiums for working-age veterans receiving benefits under the military's healthcare system, known as Tricare. It also includes cuts to major military hardware, including the Marine EFV (Expeditionary Fighting Vehicle), surface to air missiles, and one less successful variant of the F-35 fighter jet.