They wrote in a joint letter to congressional leaders that the readiness of U.S. armed forces is at a "tipping point."
A copy of the letter was provided Wednesday to The Associated Press.
The military leaders said that troops in combat and those who are being treated for wounds will get the funds needed. But the rest of the force will be severely compromised if the Pentagon has to continue operating on last year's budget.
"We are on the brink of creating a hollow force," said the letter signed by the chiefs of the Army, Navy, Air Force, Marine Corps and National Guard, as well as the chairman and vice chairman of the Joint Chiefs of Staff.
The Pentagon is facing two major money problems. First is the threat of drastic additional budget cuts if Congress and the Obama administration are unable to agree on debt-reduction measures by March. The second is Congress' failure thus far to pass a 2013 budget; that has left the Pentagon on a spending path based on its previous budget.
In their letter the military leaders said the main risk is that budget conditions will create such a wide disconnect between their spending needs and the available funds that the armed forces will be ill prepared for future combat.
"Should this looming readiness crisis be left unaddressed, we will have to ground aircraft, return ships to port, and stop driving combat vehicles in training," they wrote, adding that training would have to be reducing by almost half of what was planning just three months ago.
"To avert this crisis we urge you to take immediate action to provide adequate and stable funding for readiness," they wrote.
"Under current budgetary uncertainty, we are at grave risk of an imposed mismatch between the size of our nation's military force and the funding required to maintain its readiness, which will inevitably lead to a hollow force."
Defense Secretary Leon Panetta has been making similar arguments. Last Thursday he told a Pentagon news conference that the threat of drastic spending cuts triggered by failure to reach a debt-reduction deal by March, coupled with Congress' failure to pass a 2013 defense budget, is creating "a perfect storm of budget uncertainty."
"We have no idea what the hell's going to happen," he said. "All told, this uncertainty, if left unresolved by the Congress, will seriously harm our military readiness."
In a statement responding to the Joint Chiefs' letter, Rep. Howard P. "Buck" McKeon, chairman of the House Armed Services Committee, said Wednesday that it should serve as a "wake-up call" to Congress and the White House.
"The condition of our armed forces is swiftly declining. And this is the first red flag on what could be a hazardous road for our national security," said McKeon, R-Calif.