The budget submitted by defense Secretary Robert M. Gates has sparked a badly needed debate about America's future defense. Some hail it as prudent, but it's too prudent by half. Savings should not trump security.

He claims that his budgetary decisions reflect strategic judgments rather than cost-cutting or political pressures. Yet many of the cuts look suspect. Rather than making hard choices, he would slash programs that are unpopular with the Democratic leadership in Congress.

In defense, money should follow strategy. Guiding strategic judgments are made in two key documents: the Pentagon's Quadrennial Defense Review and the National Security Strategy from the White House. Neither has been completed.

The budget reflects Mr. Gates' belief that future wars will closely resemble the fighting in Iraq and Afghanistan - conflicts in which irregular warfare capabilities dominate. He assumes our conventional military dominance will be enough to get us through the next 10 to 15 years, allowing the Pentagon to skip some of the new weapons next up in the procurement queue.

But history is replete with mistaken assumptions about future threats. President Bill Clinton cashed a "peace dividend" in the erroneous belief that with the Cold War ended, the United States would never again face a serious threat.

What makes Mr. Gates so sure that large-scale, conventional warfare is a thing of the past? China is modernizing its armed forces at a feverish pace. Can we safely assume it won't use them against Taiwan in the next 10 years? Russia is increasingly belligerent toward Georgia and Ukraine. Can we confidently assert that it will make no military moves against them or any of our NATO allies?

We need to prepare for what others might well do, not what we think they'll do. Among other cuts, Mr. Gates caps the F-22 fighter fleet at 187; the Air Force said last fall that it needs at least 60 more to maintain air superiority against Russian and Chinese fighters. He delays the Navy's next-generation cruiser program. That could leave U.S. forward bases unnecessarily vulnerable to emerging air and ballistic missile threats. And he slashes the very capabilities we would need to defend against future North Korean and Iranian long-range missiles.

The more you examine the numbers, the harder it is to escape the conclusion that Mr. Gates is running a budget exercise and not a strategic planning process. He insists that every dollar spent to "over-insure" against some "remote" risk is a dollar not available to "take care of people, reset the force, win the wars we are in."

But this is a false dichotomy. We don't have to choose between long-term modernization and near-term capabilities. history shows we can easily afford spending 4 percent of our gross domestic product on our core defense program. Yet Mr. Gates' core defense 2010 budget comes in under that figure by $27 billion. And the budget would continue falling to 3.3 percent of GDP by 2014. defense cuts for these years could be even deeper as war costs are folded into the regular budget.

I don't doubt that Secretary Gates is sincere in his views about the armed forces we need. But it's troubling that his area of responsibility is the only main function of the administration's budget where financial prudence reigns.

We may be about to repeat a terrible mistake. President Jimmy Carter cut the defense budget by "offsetting" the high costs of military operations with restrained procurement. He invested in technologies that supposedly could provide a hedge against future threats but became nothing more than excuses to slash the procurement of ready weapons. Yes, he saved money. But we wound up with the worst of both worlds: a hollow force and a mortgage against America's military capabilities that only Ronald Reagan's military buildup would reverse.

Surely, this isn't what Mr. Gates intends. But it's what could happen if we don't prepare for the unpredictable as well as the predictable, if we fail to field armed forces that repel armies and missiles as capably as they handle terrorists and pirates.