The Obama administration plans to formally announce the enduring price tag for the Afghan forces at a NATO summit in May. (Shah Marai/AFP/Getty Images)

The U.S. military expects that sustaining the Afghan army and police forces after the planned withdrawal of American combat forces in 2014 will cost about $4 billion a year and that most of that money will have to come from the United States and other outside donors, said a senior military official Thursday.

The Obama administration plans to announce the enduring price tag for the Afghan troops at a NATO summit in May. The exact cost of paying, equipping and training the Afghan forces will depend on their size, which is the subject of debate in Kabul and Washington.

“If we are going to succeed in Afghanistan, we are going to have to make a commitment to sustaining the Afghan security forces, and my sense is that is recognized,” the senior military official said, speaking on the condition of anonymity to discuss ongoing deliberations. “That is what we are driving toward, and that is what will be announced in May at the summit.”

In recent years, the United States has spent tens of billions of dollars on Afghan forces to increase their numbers and add infrastructure. This year, the Obama administration’s budget for Afghan forces is about $11.2 billion, about twice the planned budget of $5.7 billion in 2013.

The Afghan army and police force had been expected to grow to about 350,000 troops, up from 310,000 today, but Defense Secretary Leon E. Panetta suggested this month that the goal could be scaled back to save money.

The Afghan government can afford to pay only about 12 percent of the expected $4 billion annual price tag of the Afghan forces beyond 2014, said the U.S. military official. The majority of the remaining costs would be borne by the U.S. government. U.S. officials also are counting on big contributions from NATO allies to fund the Afghan forces beyond 2014.

“I think that a 2-to-1 ratio is pretty reasonable in terms of financing,” the senior military official said regarding U.S. and European contributions.

The long-term plan for U.S. and NATO troops beyond the end of 2014 — the date set for the withdrawal of all combat troops — and the possibility of accelerating fragile peace talks with the Taliban also will be major parts of the May summit, U.S. officials said. The Pentagon expects that U.S. and NATO forces will remain in Afghanistan after 2014 to train Afghan forces and possibly carry out strikes against insurgent leaders.

The United States is seeking additional commitments from NATO at the same time it reduces its force of 80,000 troops in Europe by about 15 percent. The United States plans to eliminate two brigades of combat troops in Europe, totaling about 8,000 troops, as part of a cost-saving plan to shrink the Army to about 490,000 troops. The United States also plans to pull out an Air Force squadron and support troops.

To make up for the losses, the United States will designate a brigade to focus on Europe with the hope that it will send battalions to participate in joint exercises with the NATO allies. The Pentagon also plans to dispatch additional V-22 aircraft and about 500 Marines to Europe and move four Aegis destroyers into the area to help with missile defense.