The chairman of the Senate Armed Services Committee is warning the Obama administration that Congress could refuse to fund Afghan security forces after U.S. troops leave the country.

In an interview with The Hill, Chairman Carl Levin (D-Mich.) offered his strongest warning to Afghan President Hamid Karzai’s government, saying Kabul is “reaching beyond what is realistic” in asking that the United States guarantee it $1 billion in annual funds for security after the war. 

{mosads}But Levin’s comments also highlighted a problem to the Pentagon, which has said Afghan National Security Forces will need up to $5 billion annually to maintain operations against the Taliban and insurgent forces after the U.S. exit.

Given the U.S. budget problems and doubts about how the money will be spent in Afghanistan, that’s a hard sell for members of Congress, Levin indicated.

The chairman did not rule out supporting funding for post-war Afghan security, and said he is personally in favor of a “robust commitment” to the Afghan forces.

But Levin said he would only back the huge investment in security “if it will make a difference.”

Gen. John Allen, the commander of U.S. and coalition forces in Afghanistan, testified to Congress last month that Afghan forces will need between $4 billion and $5 billion annually to maintain operations against the Taliban and insurgent forces.

Allen has not put a timeframe on that commitment, but a House staffer estimated the United States will have to bankroll the Afghan National Security Forces entirely or partially for three to 10 years after 2014, when U.S. troops leave.

Levin said that Allen’s estimate would be peanuts compared to the roughly $30 billion to $40 billion the Pentagon spends to keep U.S. troops in Afghanistan.

Still, he and others scolded Karzai for expecting the administration to sign off on a dedicated funding stream as part of a post-war deal.

Levin said Karzai “is asking for something no president, or presidential nominee for that matter, can guarantee,” Levin said. “This is not a dictatorship.”

In a speech on Tuesday, Karzai said the United States should guarantee that his country will receive at least $1 billion in annual security funds as part of a post-war deal that Defense Secretary Leon Panetta is now negotiating with Kabul and NATO leaders.

Lawmakers are looking for ways to lower the deficit and to protect favored programs for funding. Sending billions to Karzai’s government, which has been plagued with charges of corruption, will be a difficult argument to win.

Levin said one key for him would be to make sure that Afghan leaders remain committed to the 350,000-man force they want to field initially, after American and NATO troops leave. Reports have suggested Kabul could look to reduce the size of that force after 2017.

Levin argues Afghanistan will need that size of a force to maintain security when U.S. forces leave.

“We [must] keep the size of the [Afghan] army at the size it will reach” when U.S. forces leave, Levin said.

A Republican House staffer acknowledged congressional concerns over the enduring capabilities of Afghan forces are growing as a post-war deal nears.

But the answer to the problem of supporting Afghan security forces “isn’t a guaranteed funding stream,” the staffer said.

The only way to ensure Afghan forces can fend for themselves is by focusing on their growing capabilities and the conditions on the ground, the staffer said.

A Democratic House staffer predicted a White House request for post-war security funding for Afghanistan would “trigger a vigorous debate” on Capitol Hill.

Panetta is meeting with his counterparts this week at NATO headquarters in Brussels to hammer out the details of the post-war deal, which will set the groundwork for all American and NATO involvement in the country beyond 2014.

U.S. Afghan and NATO leaders anticipate having a plan in place before the alliance’s May summit in Chicago.

On Wednesday, Panetta reiterated Levin’s claims that a financial guarantee would be out of the question in terms of locking in a deal with the Afghan government.

“You have to deal with Congress when it comes to what funds are going to be provided,” Panetta said at a press conference on Wednesday. “And we don’t have the power to lock in money for the Afghans or anybody else.”

However, Panetta pointed out the lack of a financial guarantee was not a sign that the United States would abandon the country once American troops leave in 2014.

“We’re committed to an enduring presence in Afghanistan post-2014 and a continuing effort to train, advise and assist the [Afghan security forces] in protecting the Afghan people and denying terrorists a safe haven,” he said.

Afghan defense minister Abdul Rahim Wardak said last Thursday the fiscal burden of propping up the country’s security forces “should not fall on the U.S. alone.”

But he warned if that support does not come from the United States or NATO, Afghanistan will fall back into “the catastrophic disaster of the 1990s.”

Shortly after the Soviet retreat in 1989, Washington pulled its support from the various Afghan tribes that had led the anti-Russian insurgency.

The civil war that erupted between those factions in the 1990s tore the country apart and ushered in the Taliban’s rise to power.

Jeremy Herb contributed to this report.