Adm. Michael Mullen, the nation’s top military officer, has a warning for Congressional leaders wrestling with the time frame for passing a massive war spending bill: The Pentagon is dangerously close to running out of money.

“We need [the supplemental appropriations bill] very badly before the Memorial Day recess. We stop paying soldiers on the 15th of June and we have precious little flexibility with respect to that,” Mullen, the chairman of the Joint Chiefs of Staff, said in an interview at his Pentagon office last week. “Clearly that creates incredible constraints and difficulties for us.”

Without the extra funding, Mullen said, the Defense Department would be forced to delay contract awards and withhold other spending to pay for the Iraq and Afghanistan wars. “It makes it extremely difficult to execute the day-to-day business of the Pentagon without knowing the money is coming,” he said.

It’s hardly new for the Pentagon to issue a dire warning about being strapped for cash. Defense officials in recent years have repeatedly warned of massive layoffs if supplemental spending bills were not passed.

In all cases, lawmakers approved the bills before drastic cutbacks were necessary. Nonetheless, the warnings can be a powerful political weapon in an an election year and are a concern as Congressional leaders plot a path forward on the spending bill.

Lawmakers are currently reviewing a $108 billion proposal that would cover the war costs for the remainder of fiscal 2008. While Democrats have suggested for weeks that the bill would be passed before the break, top leaders last week were uncertain as to when the bill would hit the House and Senate floors.

Senate Majority Leader Harry Reid (D-Nev.) told reporters, “I think we’ll do our best to finish this before the Memorial Day break, but if we don’t, it’s no big deal. There’s money there.” House Majority Leader Steny Hoyer (D-Md.) said late last week that he was not sure the House would be ready to consider the measure this week.

Mullen said the Pentagon could not afford to have any money cut from its request. “The $108 billion is a good number,” he said. “We have been pretty vigorous and rigorous about scrubbing that and I am comfortable with it.”

While Democrats seem to lack support to force troop withdrawals in the bill, bipartisan support is building in both chambers for a provision to force Iraqis to share more of the reconstruction costs. For example, the Senate Armed Services Committee backed a bipartisan measure in the Defense authorization bill last week prohibiting the Pentagon from paying for Iraq infrastructure projects that cost more than $2 million. A similar provision could make its way into the supplemental.

Mullen said Iraq should pay “as much as it can” of the reconstruction costs, noting Iraq has a roughly $60 billion annual surplus. Still, he said, Congress should be cautious in shifting responsibility because Iraq lacks the capacity to manage all reconstruction projects.

“Certainly it makes sense to me that … the Iraq government bear more of the financial burden of what’s going on in Iraq,” he added.

On Afghanistan, Mullen — who last month told Congress that he was “deeply concerned” about deteriorating security conditions there — predicted an even more violent year this year than last for troops on the ground as they battle insurgent forces. But he has stopped short of asking lawmakers for more troops for Afghanistan.

“Iraq is the No. 1 priority right now, and should forces become available down the road out of Iraq, then they would very likely [move] into Afghanistan,” Mullen said. He suggested as many as 12,000 more troops from the United States and other countries eventually would be needed in Afghanistan, once a contingent of 3,500 Marines leaves the country later this year.

“There will be a need for more forces down the road, but they are not going to be available unless we come down from current levels we are in in Iraq,” Mullen said, adding that the forces could include two combat brigades and 3,000 trainers for Afghan forces. He stressed that the military had yet to formally request those forces.

Some Democratic lawmakers have suggested the spending bill contain a provision calling for the military to make Afghanistan its top priority. Mullen declined to weigh in, saying Iraq remains at the top of his agenda until the president and other national leaders say otherwise.

Mullen also said he’s bullish on the future prospects for Afghanistan. “It’s going to take a long time. I do not expect an overnight success in Afghanistan. … In the long run, I am optimistic about a positive outcome,” he said.

Some lawmakers have also questioned whether the military has been “broken” by the demands of the Iraq and Afghanistan wars. Mullen disputed that claim, but he said military leaders must be vigilant to ensure troop readiness does not suffer under the strain of steady deployments.

Despite partisan bickering, Mullen also made it clear that Congress on the whole has given the military what it needs for Iraq and Afghanistan.

“I appreciate over the years that the Congress has been a terrific supporter of funding the troops for the needs that they have. There have been many supplementals, and obviously there is always a heated discussion around them. That said, in the end, Congress has provided the money for which I am really grateful,” he said.

Jennifer Bendery and Ashley Roque contributed to this report.