Updated

Defense Secretary Robert Gates plans to announce a new round of military budget cuts Thursday, a move that comes as the Pentagon prepares to build its combat force in Afghanistan by sending an additional 1,400 Marines.

The Pentagon confirmed to Fox News that the Marines will be deployed in a bid to secure gains made during the troop buildup of the past year. Pentagon spokesman Geoff Morrell said the additional force falls within the amount President Obama authorized a year ago, when he ordered 30,000 more troops to the country and gave Gates the authority to add an extra 10 percent as needed. According to the Wall Street Journal, which first reported the decision, the Marines could start arriving as early as mid-January and will be deployed mostly in the south.

The Obama administration aims to start withdrawing troops this July. But with the U.S. commitment in Afghanistan expected to last at least another three years from there, Gates is looking to find cost-savings elsewhere in the budget as Washington as a whole looks to trim the federal deficit.

The Defense Department is responsible for the biggest piece of discretionary spending in the federal government's annual budget. It's been largely protected until now, but incoming members aligned with the Tea Party movement have said that cuts to military spending must be considered.

Gates was expected to announce on Thursday that he would cancel a $13 billion plan to buy the Marines amphibious assault vehicles from General Dynamics Corp. called the Expeditionary Fighting Vehicle.

While a top priority for the Marine Corps, the EFV has long been considered a target of Gates as he looked to trim the budget. Gates has questioned whether D-Day-style landings are going to be common in future wars when the enemy is developing sophisticated weapons that can easily attack ships hovering close to shore.

Other cost-cutting measures were planned as well, including the delay of the Marine version of the F-35 Joint Strike Fighter, according to defense analysts familiar with the plan.

The steps are part of a broader effort by Gates to find some $100 billion in budget fat through 2016 that he says should be reinvested into programs for the troops and to modernize weapon systems.

According to Loren Thompson, head of the Virginia-based Lexington Institute and adviser to several major defense contractors, the Pentagon had been told to whittle its budget plan in coming years by as much as $150 billion. Thompson says that Gates was able to argue that only about $80 billion was practical.

Still, the Defense Department is being directed to create a spending plan for 2012 that doesn't exceed $554 billion, instead of the $566 billion it initially wanted. The figure does not include war spending.

Last year, Gates pledged to trim the department's bureaucracy by disbanding an entire military headquarters in Virginia, called U.S. Joint Forces Command, and cutting back on the number of general officers that staff the Pentagon.

Gates also announced that affordability would be given greater consideration when buying goods and services and that contracts exceeding $1 billion would be particularly scrutinized.

The Associated Press contributed to this report.