President Obama has asked the Pentagon to plan for a complete withdrawal of U.S. troops from Afghanistan by the end of the year amid a dispute over a security pact, but continues to leave open the possibility that some troops could remain after 2014 -- options he discussed Tuesday with Afghan President Hamid Karzai.

The White House detailed the "contingency planning" in a statement following the phone call between Obama and Karzai.

The two leaders spoke amid an ongoing dispute over a vital security agreement. That agreement would allow the U.S. to keep troops in Afghanistan after 2014, but Karzai is refusing to sign it, saying he wants his successor to sign the pact after elections this spring.

Obama and Karzai have rarely spoken in recent months, a reflection of the White House's frustration with the Afghan leader.

The White House said that Obama, in his talk with the Afghan leader, affirmed U.S. support for a "fair, credible, timely and Afghan-led" election process and vowed not to support any particular candidate. But Obama also told Karzai "that because he has demonstrated that it is unlikely that he will sign" the security pact, the U.S. is making other plans.

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"Specifically, President Obama has asked the Pentagon to ensure that it has adequate plans in place to accomplish an orderly withdrawal by the end of the year should the United States not keep any troops in Afghanistan after 2014," the White House said. "At the same time, should we have [a Bilateral Security Agreement] and a willing and committed partner in the Afghan government, a limited post-2014 mission focused on training, advising, and assisting Afghan forces and going after the remnants of core Al Qaeda could be in the interests of the United States and Afghanistan."

The White House said the administration would leave open that possibility, but added: "However, the longer we go without a BSA, the more challenging it will be to plan and execute any U.S. mission. Furthermore, the longer we go without a BSA, the more likely it will be that any post-2014 U.S. mission will be smaller in scale and ambition."

Defense Secretary Chuck Hagel said afterward that the Pentagon is indeed moving ahead, "with my strong support," with plans for a complete withdrawal.

"This is a prudent step given that President Karzai has demonstrated that it is unlikely that he will sign the Bilateral Security Agreement, which would provide DoD personnel with critical protections and authorities after 2014," he said in a statement.

The White House repeatedly has said that without a security agreement, the U.S. and international allies will have to withdraw all troops after the war formally concludes at the end of this year. The Pentagon has been pushing for the U.S. to keep up to 10,000 troops in Afghanistan after 2014.

The phone call comes a day after a top House Republican, Armed Services Committee Chairman Buck McKeon, R-Calif., delivered a scathing address about Obama's Afghanistan approach.

McKeon complained Obama has only talked about the war "a handful of times" since taking office. He charged Obama has even "openly campaigned" against his own strategy.

"So, if the president of the United States won't give this speech, I will," he said. "For the life of me, I can't figure out why the president hasn't taken credit for these victories. The gains since 2009 are three-fold -- strategic, diplomatic and moral."

The Associated Press contributed to this report.