We shouldn't gut defense. A central question of our budget debates is how much we allow growing spending on social programs to crowd out the military and, in effect, force the United States into a dangerous, slow-motion disarmament.

People who see military cuts as an easy way to reduce budget deficits forget that this has already occurred. From the late 1980s to 2010, the number of America's armed forces dropped from 2.1 million men and women to about 1.4 million.

True, Iraq and Afghanistan raised defense budgets. As these wars conclude, lower spending will shrink overall deficits. But the savings will be smaller than many expect because the costs -- though considerable -- were smaller than they thought. From fiscal year 2001 to 2011, these wars cost $1.3 trillion, says the Congressional Budget Office. That's 4.4 percent of the $29.7 trillion of federal spending over those years. In fiscal 2011, the cost was about $159 billion, 12 percent of the deficit ($1.3 trillion) and 4 percent of total spending ($3.6 trillion).

Three bogus arguments are commonly made to rationalize big military cuts.

First, we can't afford today's military.

Not so. How much we spend is a political decision. Spending on social programs replaced military spending, but that shift has gone too far.

Second, we spend so much more than anyone else that cutbacks won't make us vulnerable.

In 2009, U.S. defense spending was six times China's and 13 times Russia's, according to estimates from the Stockholm International Peace Research Institute. But China's military manpower is about 50 percent greater than ours, and it has a fighter fleet four-fifths as large. This doesn't mean that China's military technology yet equals ours, but differences in reported spending are wildly misleading.

Third, the Pentagon has so much inefficiency and waste that sizable cuts won't jeopardize our fighting capability.

Of course there is waste and inefficiency. These are being targeted in the $450 billion of additional cuts over 10 years -- beyond savings from Iraq and Afghanistan -- that President Obama and Congress agreed to this year. But like most bureaucratic organizations, the Pentagon will always have some waste. It's a myth that it all can be surgically removed without weakening the military.

Defense spending is unlike other spending, because protecting the nation is a government's first job. It's in the Constitution, as highways, school lunches and Social Security are not. We should spend as much as needed, but that amount is never clear.

Now our concept of national security -- and demands on the military -- has become expansive and murky. Aside from preventing attacks on the homeland, goals include: stopping terrorism; countering China's rise; combating cyber warfare; limiting nuclear proliferation (Iran, North Korea); averting the loss of nuclear weapons (Pakistan?); safeguarding sea routes and some major oil producers; and providing humanitarian assistance in major natural disasters.

By itself, defense spending does not ensure that our national power will be wisely or effectively deployed. This depends on our leaders. But squeezing defense will limit our civilian and military leaders' choices and expose U.S. troops to greater risk. Those who advocate deep cuts need to specify which goals -- combating cyber warfare, countering China, fighting terrorism -- should be curtailed. Would that be good for us? The world?

America's military advantage stems from advanced technology and intensive troop training. Obama repeatedly pledges to maintain America's strength, but the existing cuts may do otherwise. Even before these, defense spending was headed below 3 percent of national income, the lowest level since 1940. The need to maintain an adequate military is another reason why spending on social programs needs to be cut and taxes need to be raised.