Troop level decision adds to fiscal burden.

• Position: Budget Matters

* President Barack Obama's decision to keep more troops in Afghanistan longer than previously planned could come with a hefty price tag and lead to another budget battle with lawmakers.

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The commander in chief abandoned his plans to cut U.S. troop levels in Afghanistan to 5,500 by the end of this year. Instead, he will keep 8,400 there into 2017 to train and assist Afghan government forces, and conduct counterterrorism missions.

"The security situation in Afghanistan remains precarious," he said in July when he announced his decision.

Obama's move may require a significant amount of additional funding.

The marginal cost of deploying troops in Afghanistan has averaged about $1.2 million per year per service member, according to Todd Harrison, director of defense budget analysis at the Center for Strategic and International Studies. If that trend continues, keeping an additional 2,900 troops there through fiscal year 2017 should cost about $3.5 billion, he said in an email.

Before Obama revised his plans, his administration requested $59 billion for overseas contingency operations funding in fiscal year 2017.

"His budget does not have room for the troops he is committing," House Armed Services Committee Chairman Rep.

Mac Thornberry, R-Texas, said in a press release after Obama unveiled his decision.

"The White House must submit a supplemental funding request to accommodate troop levels in Afghanistan immediately," he said.

Harrison said there is "a good...