American troops are fighting in Iraq and Afghanistan. North Korea is launching missiles toward our allies. And Congress wants to cut defense spending.

Sounds crazy, but it's true. The House of Representatives recently passed its fiscal 2007 Defense Appropriations bill. It reduced the Bush administration's request for defense funding by $4.1 billion.

Luckily, the administration is standing its ground. President Bush has threatened to veto any measure resembling the House bill, as well he should.

Americans can -- and do -- argue about how involved Washington should be in our lives. But the federal government is required to "provide for the common defense." That's a constitutional responsibility. To fulfill it, Congress must spend money on troops and equipment.

Wait, critics may reply: The cut in the administration's defense request will be more than made up for by the $50 billion lawmakers have already provided in initial funding for wartime operations in fiscal 2007. However, this justification falls short -- for two reasons.

For one, there's virtually no way $50 billion will be enough to fund wartime operations next year. Congress will need to increase spending through a supplemental appropriations bill.

Second, there's a reason to separate the Pentagon's day-to-day war fighting budget from its long-term core defense functions: To ensure that paying for today's wars won't undercut our ability to prepare for tomorrow's military challenges. The $4.1 billion reduction in core defense funding undermines that central purpose.

Congress should realize the core functions of the defense program are essential to keeping the U.S. military the best in the world. For example, the Navy needs more attack submarines, and North Korea's July Fourth missile launches underscore the fact we must fast-track the U.S. missile-defense program. But the House bill won't accelerate production of either program.

If past practices hold true, Congress will "make up" today's underfunding in a future supplemental bill while using the $4.1 billion to fund all manner of new spending. This maneuver is one of many gimmicks that allow appropriators to evade budget caps set in the budget resolution. What seems a fiscal tradeoff is in reality just budget trickery. Theologians might call it robbing Peter to pay Paul.

Critics also could argue it isn't domestic discretionary spending that threatens to overwhelm defense spending in the long-term but the major entitlement programs -- Social Security, Medicare and Medicaid. True enough, but that's no reason to increase wasteful spending while ignoring priorities. Instead, congressional appropriators should lead by example and exercise some spending discipline.

When they do, they're likely to find defense spending already has been cut to the bone. Although the nation is at war, defense manpower is at its lowest in the last 65 years and about a third lower than in 1975. National security spending consumes only about 4 percent of gross domestic product and is projected to stay at this level or decline slightly well into the future.

Will Congress demand that Social Security, Medicare and Medicaid beneficiary rolls decline a third from current levels over the next 30 years? Will it demand that growth in these three entitlement programs not exceed overall economic growth?

These questions matter because the Bush administration's veto strategy this time around will be more difficult to execute than the one it successfully deployed for the fiscal 2006 Supplemental Appropriations bill. Then, the administration had the House on its side and was able to prevail in conference and avoid a veto. In the case of the fiscal 2006 Defense Appropriations bill, the House already has moved in the wrong direction, and the Senate is following suit.

This time, it seems likelier President Bush will have to exercise his veto. And if he does, he should then demand that Congress send him a new bill that fully funds core defense programs.

American troops today man the frontlines in Afghanistan and Iraq, preserving the liberty of the American people and protecting them from attack. Congress should ensure they have the tools to prevail. Further, this commitment should extend to the troops that will be manning the frontlines in the years ahead, as we start building the weapons and equipment they need. It's time to remind Congress of its responsibilities.

Baker Spring is the F.M. Kirby Research Fellow in National Security Policy in the Douglas and Sarah Allison Center for Foreign Policy, at The Heritage Foundation