Mitt Romney promises a major defense build-up if he is elected president. Under last year’s budget agreement, defense spending over the next decade will amount to $6 trillion. If no debt agreement is reached by January, that will drop to $5.5 trillion under rules known as sequestration. Romney, the Republican challenging President Obama, vows to spend at least 4 percent of the nation’s gross domestic product on defense, which works out to $8.3 trillion under the same economic assumptions.

Lawrence Korb warns that would be an enormous mistake. A Navy veteran who flew missions over Vietnam, he served as undersecretary of defense in the Reagan administration. He spoke last week with Star-Ledger Editorial Page Editor Tom Moran. An edited transcript appears below.

Q. How does today's defense budget compare to the budgets under President Reagan?

A. It is higher than the average under Reagan, and under (George W.) Bush when you control for inflation.

Q. Is that because of the wars in Iraq and Afghanistan?

A. No. I’m talking about the base budget. Iraq and Afghanistan operations are funded separately.

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Q. How would you compare the threat we faced, then and now?

A. You can’t compare them. The Soviet Union was a formidable military power. They had tens of thousands of nuclear weapons. They had 5 million people under arms, and very sophisticated tanks and ships. They had about 1,000 ships all over the world. They were an existential threat. As bad as Sept. 11 was — and I was in New York City then — it was not something that could destroy the United States like the Soviet Union could have.

Q. You've said the Pentagon does not have a resource problem, it has a management problem. Can you expand on that?

A. After the Sept. 11 attacks, we had what (Secretary of Defense) Bob Gates called a “gusher” of defense spending. So people did not have to make hard decisions. We spent $50 billion on weapons systems that we later canceled. And the cost grew on many others. The General Accounting Office said cost overruns on 95 major weapons systems were up to $400 billion — more than we ever had seen.

Q. Defense Secretary Leon Panetta has said the cuts that would be required under sequestration would be "catastrophic." Does that worry you?

A. Panetta is correct that if sequestration is required, it would be catastrophic because it would mean that every single item in the base budget would have to be cut by about 10 percent. But if you cut the overall defense budget by 10 percent from the current level of $550 billion and do it in a strategic way, that would not be devastating. That would return the base budget, adjusted for inflation, to the amount we spent in 2007. And I do not remember anyone complaining about how little we were spending on defense then.

I’ve seen that Mitt Romney said we’ll have the smallest Navy since 1916, the smallest Air Force since it was created and an Army that’s as small as it was before World War II. But you have to put that in context. We’ll have fewer ships than in 1916, but we’re bigger than the next 11 navies combined. And if you look at the Air Force, we have a new generation of fighters, the fifth generation, that nobody else has — the F-22s and F-35s. And we have more fourth-generation fighters than the rest of the world combined. Remember, too, that the Air Force is relying more and more on unmanned aircraft these days.

So if you just count numbers, you miss the full picture. The problem is not that our Army is too small; the problem was that, in 1941, Hitler’s army was too damn big.

Q. So our relative position is stronger than ever?

A. Yes. In 2001, we accounted for one-third of the world’s military spending and one-third of the world’s GDP. By 2010, we were up to almost 50 percent of military spending, and our share of GDP was down to 20 percent.

Q. Let’s talk about ways to safely reduce defense spending. You’ve discussed shrinking our nuclear arsenal, for one.

A. We have 5,133 nuclear weapons, and the START agreement will take us down to 1,550 warheads and 700 delivery systems. The (U.S. Air Force) Air War College — not some liberal think-tank — says that for deterrence, you don’t need more than 311 warheads. Gen. (James) Cartwright, who was vice chairman of the Joint Chiefs, says you don’t need more than 800. So you can easily cut below even the number under START.

If you don’t, you have to modernize all three legs of the triad (submarines, missiles, bombers). A new generation of 12 submarines to launch ballistic missiles would cost you at least $100 billion just for the boats. You’d have to build a new generation of bombers. The Air Force chief of staff said that if they cost more than $550 million each, we should cancel it, and if you made that number, it would be quite surprising. So even if you take Cartwright’s number, you wouldn’t have to spend a couple of hundred billion to modernize your arsenal.

Q. What else?

A. I don’t think the Navy should buy the F-35 Joint Strike Fighters. It is one plane with three missions. The Air Force can land it on land, the Navy on carriers, and the Marines could use vertical take-off. When you try to get one plane to do these three things, you run into many technical and cost problems.

Q. So part of the problem is that each branch of the military wants its own capabilities, rather than rely on the other? That kind of competition drives up costs?

A. Yes.

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Q. Other examples?

A. I would stop production of the V-22, which takes off like a helicopter and flies like a plane. (Former Vice President) Dick Cheney tried to cancel it and was stopped by Congress. Thirty people have died developing them. And we have 180 — that’s enough.

Q. Can we cut costs by reducing our footprint abroad?

A. Definitely, particularly in Europe. Obama’s plan is to reduce our troops in Europe from 80,000 to 73,000. But you can easily get to 40,000. There’s no military threat and the Europeans have become free-riders. Romney said in his speech that he wants them to spend 2 percent of their GDP on the military. Good luck. They’re not going to do that.

Q. How about within our borders?

A. Very definitely. Secretary Panetta has asked for another base-closing commission and Congress hasn’t authorized it.

Q. Where else could we save?

A. No one wants to do this, but we could reduce benefits for military retirees. We haven’t raised their health care premiums since the 1990s. And when they reach 65 and get Medicare, the military gives them TRICARE, which picks up everything that Medicare doesn’t. The health care budget for the Pentagon was over $50 billion this year.

Q. If the budget is cut like this, where would we be vulnerable?

A. I don’t see how we would be. If you are threatened by terrorists with global reach, I don’t see how an aircraft carrier is going to help you. And look at China. Romney says we have to increase the Navy budget, but our Navy budget alone is larger than the total Chinese military budget. So if we go back to the 2007 levels of spending, I don’t see any vulnerability if you make the hard choices and spend it correctly.

Q. Let's talk about the politics: Why are we spending more than we should?

A. After 9/11, there was a sense of panic and nobody wanted to ask the hard questions. The military, which always wants more money, took advantage of that. But if you look at opinion polls, even Republicans say you can cut it.

Q. This sounds like a triumph of the military-industrial complex that President Eisenhower warned about.

A. Sure. These guys have gone over the line this time, trying to scare people that all the jobs will be cut. That’s nonsense. Even if you had sequestration, defense contractors wouldn’t feel the impact for a couple of years.

The way the defense budget works is, you get authorization to spend and up to five years to actually spend it. They have $90 billion authorized that hasn’t been spent. And we sell weapons abroad. This year, we had 87 percent of that market, about $66 billion.

Q. Romney's plan to spend at least 4 percent of GDP on military would mean spending would increase to $8.3 trillion over 10 years, compared to $5.5 billion under sequestration. Is he serious, or is that campaign rhetoric?

A. I think it’s campaign rhetoric.

Q. If he did that, would we be spending more in real terms than we did under Reagan?

A. Much more, even if you control for inflation. I worked in his administration, and people forget that defense spending increased 28 percent over the first four years, but was cut by 10 percent over the next four. So you had about a 2 percent annual increase in real terms.

Q. If Reagan were president today, would he cut the military budget?

A. Yes, he would. Because in his second term, he saw the need for cuts, given the deficit and the build-up we had done. And the build-up over the last 13 years has been bigger than his was.