* U.S., NATO says Karzai's objections may force pullout
* Obama has ordered Pentagon to plan for possible exit
* Late decision could pose problems closing bases (Adds comments by NATO's top military commander)
By Adrian Croft and Justyna Pawlak
BRUSSELS, Feb 27 (Reuters) - NATO defence ministers agreed on Thursday to plan for all options for the alliance's future presence in Afghanistan including a possible pullout of all its troops this year, NATO chief Anders Fogh Rasmussen said.
With foreign troops due to end combat operations in Afghanistan at the close of 2014, NATO has been planning to keep a slimmed-down force there to train and assist Afghan forces who continue to battle Taliban insurgents.
But NATO and U.S. officials say President Hamid Karzai's refusal to sign an agreement with the United States creating a legal framework for U.S. troops to stay in Afghanistan could force it to pull out all its troops by the end of the year.
"Today we agreed the need to plan for all possible outcomes including the possibility that we may not be able to deploy to Afghanistan after 2014 due to the persistent delays we have seen," NATO Secretary-General Rasmussen told a news conference.
On Wednesday, Rasmussen said he still hoped plans to keep troops in Afghanistan beyond this year could be salvaged. But President Barack Obama has told the Pentagon to prepare for the possibility that no U.S. troops will be left in Afghanistan because of Karzai's refusal to sign the accord.
With an election due in April, NATO officials still hope Karzai's successor could sign the agreement.
"Let me be clear that this is not the outcome we want," Rasmussen said, referring to the option of no NATO troops staying behind in Afghanistan after this year.
"It is not the outcome we think is in the interest of the Afghan people. However, it might be the unfortunate outcome if there is no security agreement in due time. This is what is at stake."
The NATO-led force in Afghanistan has a current strength of more than 52,000 soldiers, including 33,600 U.S. troops.
Under NATO's preferred plan for a post-2014 training mission, that force would be cut to 8,000 to 12,000 soldiers, headquartered in Kabul with four regional bases.
Without going so far as a total pullout, dubbed the "zero option", NATO could also look at scaling back that plan and retain a smaller force just in the capital, diplomats say.
NATO's top military commander, U.S. Air Force General Philip Breedlove, said on Thursday he and U.S. General Joe Dunford, who commands U.S. and allied forces in Afghanistan, both very strongly supported the original plan for the post-2014 mission.
"That is the mission that we have planned and embraced and I think provides the best future for Afghanistan and that is the mission we hope to execute," he said in an interview with Reuters and The Wall Street Journal.
He said NATO commanders have already planned the drawdown of NATO forces in Afghanistan this year to give political leaders flexibility "all the way through the year" to either leave enough forces for the new training mission or to pull out altogether.
But Breedlove, NATO's Supreme Allied Commander Europe, said a decision "very late in the fall" to quit Afghanistan entirely could create problems in closing down major military bases such as Kandahar in the south or Mazar-i-Sharif in the north.
"If we get a very late decision on those large bases, we won't be able to get all the kit out, but we will get all of the high value (equipment), what we really want to bring out.
"You just can't say on December, you know, whatever your date, close Mazar-i-Sharif in three days. It is not going to happen," he said. (Additional reporting by Phil Stewart; Editing by Mark Heinrich)