Defense Secretary Chuck Hagel warned key lawmakers on Wednesday that slashing $52 billion from the Pentagon’s budget next year if across-the-board budget cuts remain in effect would have “severe and unacceptable effects.”

The defense chief also said Congress should “become a full partner in ending business-as-usual practices” that defense officials think have bloated parts of the Pentagon budget unnecessarily, as lawmakers have worked assiduously to protect jobs and programs in their districts.

“We urgently need Congressional support in enacting difficult but necessary measures,” Hagel wrote in a letter to Sen. Carl Levin (D-Mich.), the head of the Senate Armed Services Committee, and Sen. James M. Inhofe (R-Okla.), the panel’s ranking member. “If the cuts continue, the Department will have to make sharp cuts with far reaching consequences, including limiting combat power, reducing readiness and undermining the national security interests of the United States.”

The Pentagon’s proposed 2014 budget was drafted under the assumption that the drastic reductions known as sequestration, which requires even cuts across the federal budget, would be replaced by a more flexible, sensible plan. But an alternative to sequestration is appearing increasingly unlikely because the consequences of cuts so far have been less dire than the ominous predictions federal agencies made last year.

Hagel’s letter was submitted in response to a request from Levin and Inhofe, who asked the Pentagon in May to outline how it would grapple with the $52 billion shortfall if sequestration remains in place after the end of the fiscal year.

Slashing payroll substantially next year is not a viable option, the Pentagon said in its assessment, because service members who are let go are entitled to separation payments, travel costs and unemployment insurance. This year’s sequestration cuts forced the Pentagon to furlough hundreds of thousands of employees for 11 days.

If it becomes clear that sequestration will remain in place for years to come, the Pentagon would need congressional approval to trim the size of the army and other services in future years. Such a possibility “raises the unfortunate prospect of forced separations of personnel who have recently served in Afghanistan,” the budget contingency plan said.

The $52 billion cut would continue to take a toll on training and infrastructure, the Pentagon warned, and squeezing the budget further will lead to a loss of jobs and a disruption of “community life” in areas near military bases.

“A military that prides itself on technical superiority would increasingly have to ask its workforce to labor in substandard facilities,” the budget blueprint said.

Furthermore, the Pentagon warned, the readiness of special operations units would erode, and the Air Force would be forced to further cut training for fighter pilots.

Inhofe said in a statement that he had hoped the Pentagon’s analysis would include more details.

“As I predicted, sequestration is leading to the hollowing out of our military and if the Department of Defense’s sequestration is not averted for future years, we will move beyond furloughs and programmatic reductions to firing personnel and canceling our critical weapons programs.”