In a sharply-worded statement, Defense Secretary Leon Panetta laid into the House Republican plan during a briefing with Joint Chiefs of Staff Chairman Gen. Martin Dempsey at the Pentagon.
The plan, crafted by House Republicans, would shave $243 billion from the national deficit, mostly on the backs of social welfare programs.
Proponents argue the plan would spare the Defense Department a $250 billion budget cut over the next five years.
Reasserting that the national debt cannot be shouldered by defense cuts alone, Panetta argued that neither should it be squared "by taking these funds from the poor, middle-class Americans [and] other vulnerable parts of our American constituencies."
"It is not balanced. It is not fair," he added regarding the House GOP plan.
The Pentagon chief also had some stern words for House lawmakers, who passed their version of the fiscal 2013 Defense authorization bill early Thursday morning.
The $643 billion spending package includes billions of dollars for missile defense programs and for keeping several weapons systems DOD had pegged for retirement in the U.S. arsenal.
The Pentagon budget sent to Capitol Hill in February represented a delicate balance between the department's dire fiscal situation and its need to meet critical national security demands, Panetta explained.
"When Congress restores funds to protect particular constituencies ... then they risk upending the kind of careful balance that we've worked very hard to achieve," Panetta said.
For his part, Dempsey said DOD and Congress must "make sure our armed forces have what they need and no more than what we need" to keep U.S. national security priorities intact.
"Before giving us weapons we don't need or giving up on reforms that we do need, I would only ask to make sure it's the right choice, not just for our armed forces, but for the nation," the four-star general said.
With the Senate set to begin marking up its version of the fiscal 2013 defense bill, Panetta pleaded for cooperation between Capitol Hill and the Pentagon.
As the budget debate continues, both sides must recognize "the budget realities that we face, not the ones that some would like to pretend are not there," he said.
"If Congress now tries to reverse many of the tough decisions that we reached . . . then they risk not only potential gridlock [but] ... they could force the kind of trade-offs that could jeopardize our national defense," Panetta said. "There is no free lunch here."