By Phil Stewart and Missy Ryan
WASHINGTON (Reuters) - The U.S. military could wait months for a political decision on whether troops stay or leave Afghanistan, but delaying a security pact would damage the confidence of Afghan forces and undermine NATO's plans, the top U.S. military officer said on Wednesday.
The comments by General Martin Dempsey, chairman of the U.S. military's Joint Chiefs of Staff, came amid an impasse over the security pact, which would allow American troops to stay in Afghanistan beyond the end of 2014.
President Barack Obama's administration has said the pact needs to be signed this year, despite resistance from Afghan President Hamid Karzai, who has suggested the deal might not be concluded before presidential elections in April 2014.
Dempsey also said the pact "really needs to be done now."
But he added that the U.S. military's logistical constraints weren't the main obstacle, warning of other factors, such as the need by many allies - some of whom need parliamentary approval for any future troop presence - to make plans soon. A delay would also erode the confidence of Afghan security forces as they fight a still-potent Taliban insurgency, he said.
"We're not the limiting factor," Dempsey told a Pentagon news conference when asked how long he would need logistically to get troops out of Afghanistan by the end of 2014.
"We wouldn't be to a level where it would begin to affect the options (facing the U.S. military) until probably early summer," he added.
The United States has 46,000 troops in Afghanistan, but that figure is set to fall to 34,000 by early 2014.
Dempsey noted that the Afghan mission included some other NATO nations "who have a different set of requirements to make their decisions" regarding their troops contributions. There are approximately 27,000 non-U.S. NATO-led troops in Afghanistan.
"So, we will see an erosion of the coalition," he said.
"And by the way, the other thing we will see is an erosion of confidence by Afghan security forces as they begin to be anxious - literally - about whether we're there to support them."
Dempsey said that while Afghan forces were capable as they battle the Taliban, they weren't yet confident.
"It really needs to be done now, mostly because what's hanging in the balance in Afghanistan is confidence."
Last month, Karzai suggested he might not sign the security pact until after national elections next spring. He has since demanded that foreign forces put an immediate end to raids on Afghan homes and that the United States repatriate all Afghan detainees at its military prison in Guantanamo Bay, Cuba.
There are fears that April elections, which will bring Afghans their first new leader since 2001, could be delayed or drag out if a run-off occurs.
A U.S. defense official, speaking on condition of anonymity, said delays in finalizing the security pact could damage international support critical to any NATO military presence beyond 2014, when the NATO combat mission ends.
"It's not just a matter of moving troops in and out; it's about keeping an international network of support to provide money and security support to Afghanistan," the official said.
U.S. Secretary of State John Kerry on Tuesday said the bilateral security agreement (BSA) could be signed by Karzai's defense minister, Bismillah Khan Mohammadi, effectively circumventing Karzai.
But Karzai's spokesman said the Afghan leader would not allow any of his ministers to sign the BSA unless key demands were met first.
Dempsey said it was important that any agreement be binding. "As long as the document is considered legally binding by both parties and credible internationally, then I think it will be a matter of who they decide signs it," he said.
(Editing by Paul Simao)