President Obama has determined that Afghan President Hamid Karzai is unlikely to sign a bilateral security agreement, the White House said. (Charles Dharapak/AP)

President Obama has ordered the Pentagon to begin formally preparing for a complete withdrawal of U.S. troops from Afghanistan by the end of this year, Defense Secretary Chuck Hagel announced Tuesday, signaling that the Obama administration increasingly sees that as a possible outcome.

The order, Hagel said in a statement, came after Obama determined that it is unlikely that Afghan President Hamid Karzai will sign a long-delayed bilateral security agreement, “which would provide [Defense] personnel with critical protections and authorities after 2014.”

Hagel’s comments came after Obama telephoned Karzai on Tuesday morning to convey the same message. In its own statement, the White House said that because Karzai “has demonstrated” that he does not intend to sign the agreement, the Pentagon has been instructed “to ensure that it has adequate plans in place to accomplish an orderly withdrawal . . . should the United States not keep any troops in Afghanistan after 2014.”

Obama left the door open, however, for Karzai’s successor — to be chosen in April elections — to sign the pact. “Should we have . . . a willing and committed partner in the Afghan government,” the White House said Obama told Karzai, a “limited” training and counterterrorism force would be in the interests of both countries.

But “the longer we go without a BSA,” or bilateral security agreement, “the more likely it will be that any post-2014 U.S. mission will be smaller in scale and ambition,” the White House said.

Obama has not decided how many troops he is willing to leave in Afghanistan after the full combat withdrawal, scheduled to be completed by the end of December. Options under consideration include 10,000, together with 5,000 NATO and other international troops, to remain until the end of 2015 at bases around the country; a somewhat smaller number, based primarily in Kabul, with the ability to travel as needed; 3,000 U.S. troops restricted to bases in Kabul and Bagram; and a complete withdrawal.

Hagel told NATO partners late last year that he was hopeful Karzai would sign the document by this week’s NATO defense ministers meeting. NATO foreign ministers, who have said they will leave no troops in Afghanistan without a robust U.S. presence, are likely to reinforce those views when Hagel meets with them in Brussels on Wednesday.

The military has made clear its strong preference for the 10,000-troop option, as have the State Department and the CIA.

Although the Pentagon had been informally looking at what a “zero option” would mean, “we were not actively planning for a complete withdrawal,” said Rear Adm. John F. Kirby, a Pentagon spokesman. “And now we will.”

Rep. Adam Kinzinger (R-Ill.), a former Air Force pilot who served in Afghanistan, criticized the decision to start planning for a full pullout, saying the move jeopardizes hard-won gains made over the past decade. In a statement, he said, “President Karzai may be a difficult partner, but we owe it to the Americans who gave their lives for our cause to seek the best resolution available.”

Ernesto Londoño contributed to this report.