Defense Secretary Panetta is warning Congress that additional Pentagon budget cuts that would be triggered if the Super Committee fails  to reach a deal by  next week could lead to significant military cutbacks, including the possible termination of the Joint Strike Fighter program and the end of America’s land-based nuclear missile fleet.

The Pentagon is already working its way through more than $450 billion in cuts over the next 10 years, but Panetta is concerned about a further round of $600 billion in cuts that would be automatically triggered if the super committee fails to trim $1.2 trillion from the federal debt.

In a letter to Republican Senators  John McCain of Arizona and Lindsey Graham of South Carolina, Panetta for the first time provided specifics about what the cuts might mean for the Pentagon.

“The impacts of these cuts would be devastating for the Department,” Panetta wrote.  McCain and Graham had asked the defense secretary to provide them with specific information beyond his general warnings about the harmful potential impact of the second round of cuts.

Panetta said a further round of cuts would lead to a combined 23 percent or $100 billion in Defense spending cuts in fiscal year 2013.

“A cut of this magnitude would be devastating in itself, but it gets worse ” because by law that cut “would have to be applied equally to each major investment and construction program,” Panetta said.

Such a cut would “render most of our ship and construction projects unexecutable –you cannot buy three quarters of a ship or a building and seriously damage other modernization efforts,” he said. The DOD civilian workforce would also be affected, as they might have to face month-long furloughs to save on personnel costs.

However, there would also be significant long-term costs that would leave the United States with the smallest ground force since 1940, a Navy of 230 ships that would be the smallest since 1915 and would leave the Air Force with the smallest number of tactical fighters in its history.

Included in Panetta’s response was a document entitled “Effects of Sequestration on the Department of Defense” that includes a list of big ticket weapons programs and systems that might be directly affected by another round of Defense spending cuts.

This includes the possible termination of the Joint Strike Fighter program, where the Pentagon plans to purchase 2,443 of the aircraft as the next-generation fighters for the Air Force, Navy and Marines.   The program has already suffered from rising costs and production delays.

Another cut is simply listed as “eliminate ICBM leg of Triad” that would have a significant impact on America’s long held nuclear strategy of a “nuclear triad” or a nuclear arsenal of strategic bombers, Inter Continental Ballistic Missiles (ICBM) and submarine launched ICBMs.

Eliminating the land-based ICBMs would still likely leave enough air-launched and sub-launched nuclear weapons to serve as a  nuclear deterrent.  However, eliminating the ICBM fleet would represent a cut that Panetta has opposed in the past.

Appearing before the House Armed Services Committee a month ago, he suggested he would be opposed to unilateral cuts to the nuclear arsenal.

“I don’t think we ought to do that unilaterally,” he said. ”We ought to do that on the basis of negotiations with the Russians and others to make sure that we are all walking the same path.”

The cuts could potentially force the services to end significant modernization plans.  The Navy would be left with only 10 ballistic missile submarines and its new Littoral combat ships program would come to an end. The Army’s plans to modernize its helicopters  and ground combat vehicles would also be terminated.  The Air Force’s plans for a next generation bomber would also be done away with.

The cuts would also affect plans to deploy a missile defense shield for Europe, a major initiative designed to counter a ballistic missile threat that might be posed by Iranian long-range missiles.

Funding for the war in Afghanistan would not be directly affected, as those funds  are exempt from the sequestration, but the impact on the base budget could still cause problems with late contracts and delayed payrolls.