Defense Secretary Chuck Hagel provided on Wednesday a summary of the Pentagon’s contingency plan for next year if Congress doesn’t find a way to stop “sequestration” budget cuts, warning of sizable cuts to investment accounts.

PentagonSequestration–the decade-long $1.2 trillion cut to defense and non-defense spending that started in March–would tap $52 billion from the Pentagon’s coffers in fiscal year 2014 if lawmakers remain at odds over if and how to stop the reductions, Hagel wrote Wednesday to Senate Armed Services Committee (SASC) Chairman Carl Levin (D-Mich.) and Ranking Member James Inhofe (R-Okla.).

“I strongly oppose cuts of that magnitude because, if they remain in place for FY 2014 and beyond, the size, readiness and technological superiority of our military will be reduced, placing at much greater risk the country’s ability to meet our current national security commitments,” the defense secretary wrote in a letter accompanying a five-page sequestration contingency plan for FY ’14.

Hagel warned that sequestration would create “severe and unacceptable effects” on the military in the fiscal year that starts Oct. 1. And those would occur even if Congress gives the Pentagon more flexibility in how to apply the across-the-board sequestration cuts, he said.

“Flexibility in this instance would mean that Congress approves program cuts denied in the past and allows reallocation of funding, without regard to existing budget structures or limitations on transfer authority,” Hagel said, calling the cuts “too steep and abrupt to be mitigated by flexibility, no matter how broadly defined.”

The defense secretary said a $52 billion cut in FY ’14 would compel the Pentagon to again impose hiring freezes and reduce facilities maintenance, as well as “consider involuntary reductions-in-force to reduce civilian personnel costs.” Such a cut would hit training and overall readiness, which he said would remain at current low levels or further decline.

Hagel pointed out that the Pentagon would not be able to substantially reduce military personnel funding in FY ’14 “without draconian actions”–a situation that puts pressure on other parts of the Pentagon budget.

“The difficulty of substantially reducing military personnel funding in FY 2014 would likely require disproportionately larger cuts in the (Defense) Department’s investment accounts–assuming flexibility in implementing changes, cuts of 15 to 20 percent would be common,” he wrote. “The resulting marked slowdown in modernization would reduce our long-term, critically important and historic technological superiority and undermine our better buying power initiatives.”

Hagel called on Congress to help the Pentagon with this budget quandary by “ending business-as-usual practices–in areas such as infrastructure, benefits and procurement–that would otherwise require further cuts to readiness, modernization and combat power.” He said the Pentagon “urgently” needs congressional support in making difficult changes, including retiring “some lower-priority weapons, including Navy ships and Air Force aircraft.” He called for cost-saving moves including allowing the Pentagon to end programs such as the C-27 aircraft.

He warned if Congress does not help the Pentagon in the ways it wants, more cuts in modernization, readiness, and combat power will be needed to accommodate the $52 billion in sequestration cuts along with future reductions.