WASHINGTON -- The Marine general selected to command United States and allied forces in Afghanistan acknowledged Thursday that he has been left out of the planning for troop reductions and does not know what combat commanders consider a necessary number of troops to bring the war to a successful conclusion.

The admission by Marine Gen. Joseph F. Dunford during his nomination hearing, appeared to flabbergast Sen. John McCain (R-Ariz.), ranking Republican on the Senate Armed Services Committee and a vitriolic critic of the Obama administration's intention to gradually reduce the 68,000 U.S. troops now serving in Afghanistan.

Dunford also said U.S. military forces will be needed in Afghanistan after 2014. He specifically included fighter jets and attack helicopters, intelligence drones and special forces counterterrorism squads as well as advisers and trainers. But he did not name a specific number of troops he believes would be required.

Obama has vowed to bring home all combat troops by the end of 2014. The White House this week is weighing recommendations from Gen. John Allen, currently the top commander in Afghanistan, on whether and how quickly troop levels can be reduced before then. The level of U.S. commitment after 2014 will in part be determined by a U.S.-Afghan bilateral security agreement, which officials began negotiating this week.

Obama had nominated Allen, also a four-star Marine general, to move from his Afghanistan command to become NATO commander. But that nomination is on hold while the Pentagon inspector general investigates email and other ties between Allen and Jill Kelley, a Tampa socialite.

The nomination of Dunford, currently assistant Marine Corps commandant, to be Afghan war chief is likely to be approved, and he is scheduled to take over the job in February. He would assume command of all U.S. and allied forces at a turbulent period in Afghanistan, with critical presidential elections there scheduled for late 2014 and U.S. forces already turning from combat to an advisory role with Afghan security forces.

The 1st Cavalry Division's 1st Brigade, normally a fighting unit of about 3,500 soldiers, just arrived in Afghanistan with about 1,500 troops divided into teams of a dozen or more specialists to operate inside Afghan army units as advisers. The brigade is the first of the newly reorganized security force assistance brigades now deploying to Afghanistan to replace purely combat brigades, a 4th Brigade officer, Maj. Steven L. Miller, said in an email Thursday.

These teams are responsible for advising Afghans during operations and linking them with U.S. air cover, intelligence and logistics capabilities.

As in past hearings on the now 11-year-long war, an air of pending disaster hung over the proceedings, with several senators using the word "bleak" to describe the chances that the United States can manage to extricate itself cleanly from Afghanistan.

McCain told Dunford that the U.S. campaign in Afghanistan "is at a very serious and troubling crossroads." In addition to the rising number of "insider attacks" by Afghans on Americans, McCain charged that ineffectiveness and corruption of the Afghan government and "fundamental doubts about American resolve'' have already enabled Taliban battlefield victories and allowed al Qaeda to begin re-establishing itself inside Afghanistan.

Unless U.S. troop strength is held at 68,000, McCain said, the White House war policy amounts to "a rush to failure."

Asking point-blank whether Dunford agreed with what McCain said was the unanimous position of combat commanders to hold the troop level at 68,000, Dunford replied: "I have not been included in those conversations." Appearing stunned, McCain shot back: "Do you feel prepared?"

As Dunford started to answer, McCain interrupted. "So you are a blank slate," he said, turning away.

But Dunford defended the military's work in Afghanistan, saying that progress has been made and levels of violence have been sharply reduced in the areas where security has been taken over by Afghan security forces.

"Violence today is largely outside the populated areas because the Afghan security forces have secured the populated areas," Dunford said. He said the Taliban has had "significant leadership losses over the past few year -- the average age of their leadership now is probably 20 years younger because they've had significant attrition. They are suffering financial difficulties and clearly they did not achieve their objectives in 2012."

But he nodded grimly when Sen. Susan Collins (R-Maine) noted her "deep concern" about Afghans in government uniforms killing American troops. "This is absolutely devastating to families of American service members, since they are trying to help and being killed by them is just devastating."

Dunford also acknowledged that Afghan government corruption also remains a critical problem.

"I don't for a minute understate the challenges associated with this endeavor," he said.

Since U.S. forces invaded Afghanistan in the wake of the 9/11 terrorist attacks, 1,705 American military personnel have been killed in battle, according to the latest Pentagon data. The toll of wounded has reached 18,007.

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  • Start of War: Oct. 7, 2001

    <em>American soldiers hide behind a barricade during an explosion, prior to fighting with Taliban forces November 26, 2001 at the fortress near Mazar-e-Sharif, northern Afghanistan. (Photo by Oleg Nikishin/Getty Images)</em>

  • Number of U.S. Troops in Afghanistan: 88,000

    <em>US Marines with the 26th Marine Expeditionary Unit deployed from the USS Bataan's Amphibious Ready Group arrive December 14, 2001 at an undisclosed location with field gear and weapons. (Photo by Johnny Bivera/Getty Images)</em>

  • Number of Troops at War's Peak

    <em>U.S. Marines begin to form up their convoy at a staging area near Kandahar, Afghanistan, as they await orders to begin their trek to Kandahar to take control of the airfield 13 December, 2001. (DAVE MARTIN/AFP/Getty Images)</em><br><br> Number of U.S. troops in Afghanistan at the war's peak: About 101,000 in 2010. Allies provided about 40,000.

  • Withdrawal Plans

    <em>U.S. President Barack Obama delivers a televised address from the East Room of the White House on June 22, 2011 in Washington, D.C. (Pablo Martinez Monsivais-Pool/Getty Images)</em><br><br> Withdrawal plans: 23,000 U.S. troops expected to come home by the end of the summer, leaving about 68,000 in Afghanistan. Most U.S. troops expected to be out of Afghanistan by the end of 2014, though the U.S. is expected to maintain a sizeable force of military trainers and a civilian diplomatic corps.

  • Number of U.S. Casualties

    <em>American flags, each one representing the 4,454 American soldiers killed in the Iraq and Afghanistan wars, move in the breeze at The Christ Congregational United Church March 17, 2008 in Miami, Florida. (Photo by Joe Raedle/Getty Images)</em><br><br> Number of U.S. casualties: At least 1,828 members of the U.S. military killed as of Tuesday, according to an Associated Press count. According to the Defense Department, 15,786 U.S. service members have been wounded in hostile action.

  • Afghan Civilian Casualties

    <em>Asan Bibi, 9, sits on a bench as burn cream is applied to her at Mirwais hospital October 13, 2009 Kandahar, Afghanistan. She, her sister and mother were badly burned when a helicopter fired into their tent in the middle of the night on October 3rd, according to their father. (Photo by Paula Bronstein/Getty Images)</em><br><br> Afghan civilian casualties: According to the United Nations, 11,864 civilians were killed in the conflict between 2007, when the U.N. began reporting statistics, and the end of 2011.

  • Cost of the War

    <em>An Iraqi man counts money behind a pile of American dollars in his currency exchange bureau in Baghdad on April 11, 2012. (ALI AL-SAADI/AFP/Getty Images)</em><br><br> Cost of the war: $443 billion from fiscal year 2001 through fiscal year 2011, according to the Congressional Research Service.

  • Number of Times Obama Has Visited Afghanistan

    <em>US President Barack Obama speaks to troops during a visit to Bagram Air Field on May 1, 2012 in Afghanistan. (MANDEL NGAN/AFP/Getty Images) </em><br><br> Number of times Obama has visited Afghanistan: 3 as president, including Tuesday, and 1 as a presidential candidate.