A fight is brewing in the U.S. military between manpower and technology. With the economy cratering and defense budgets flattening, we can no longer afford both large armies meant to pacify hostile populations, and legions of high-end air and naval platforms that fulfill our technological dreams. Because of the powerful political backing those high-end platforms enjoy, this budget conflict might spark a broad backlash to our recent fascination with wars of occupation.

Our fetish for counterinsurgency campaigns has now made us a land power. We reacted to the wars in Afghanistan and Iraq by expanding the ground services, even as the cost of manpower skyrockets. That investment is likely to increasingly crowd out the budgets of the Navy and Air Force, which employ most of our high-technology platforms. Indeed, Secretary of Defense Robert Gates’ budget recommendations, announced this week, would delay the Navy’s next-generation cruiser and its aircraft carrier build schedule. It also proposes the end of the Air Force’s F‑22 and C‑17 programs and the indefinite delay of the next-generation bomber.

Manpower costs already take a growing chunk of the defense budget each year, and that’s before the substantial increases in family support and medical care announced in this week’s budget recommendations. According to the Congressional Budget Office, the cost in pay and benefits per active-duty troop rose 45 percent above inflation from 1998 to 2009, from $55,000 to $80,000. Congressionally authorized increases in salary — political gold in wartime — has amounted to around 3 percent annually. Health care coverage costs for active troops, which is paid for from the operations and maintenance account, is also experiencing massive cost-growth per service-member.

These costs have encouraged the Navy and Air Force to shed a combined 80,000 active-duty personnel over the last decade, although Gates’ budget recommendations call for an end to the two branches’ force reductions. Meanwhile, the ground forces have been growing and may continue to do so. The Army will comprise 547,000 troops by the end of the year — 60,000 soldiers more than in 2005. Army leaders want another 30,000 on top of that. The Marines will have grown by 28,000 over the same period, to a total of 205,000.

The idea behind this growth is that our counterterrorism objectives now require a series of counterinsurgency campaigns. We are told that terrorists threatening the U.S. flourish in failed states — what we used to call states engaged in civil wars — therefore U.S. security depends on pacifying and stabilizing those states.

According to Army doctrine, doing so requires a high ratio of counterinsurgents — whether native or foreign — to population. One to 50 is the most cited figure, a daunting requirement in countries like Iraq and Afghanistan, each with around 30 million people. According to this logic, because occupying these two medium-size countries at ratios far lower than best practice has overwhelmed our forces, we need to grow the Army, probably even beyond the current expansion.

The increased size of the ground forces heightens the pressure that personnel costs put on the rest of the defense budget. War supplementals and a rapid growth in nonwar defense spending — nearly doubled since 1998 — previously limited this conflict. But decreasing tax revenues, fiscal stimulus and bailout packages, and possible health care reform mean that growth in defense spending will in all likelihood halt. The Obama administration claims it will increase military spending only by inflation for the next decade. Some Congressional leaders even want cuts.

Other defense accounts will now have to fund rising personnel costs. If Gates’ budget recommendations are any indication, the main source of the needed windfall will be cuts in spending that is more elastic than operations and maintenance — namely, development and procurement of new weapons and vehicles. Should Gates’ budget make it through Congress unscathed, cancellations and slowdowns will hit most big-ticket programs in the next few years.

But if budgets stay flat, even a drastic procurement trimming will not produce enough savings to sustain an enlarged Army and Marine Corps. That will probably require shrinking the budgets of the Navy and Air Force, which means cutting force structure — air wings and carrier battle groups (one is now scheduled to be eliminated by 2040), and the support apparatus behind them.

Cuts to forces structure would, in turn, outrage the services that rely on units for promotion opportunities, as well as the Congressmen who rely on Navy and Air Force spending for local jobs. Their outrage could rejuvenate old-fashioned American discomfort with nation-building. Sept. 11 drove that discomfort from Congressional hearing rooms and the campaign trail. But as is often the case in politics, where ideas lie dormant until powerful interests need them, it did not disappear from academic texts and the occasional op-ed.

Defenders of high-technology programs will now have an interest in arguing, as political scientists have been doing for some time, that occupations of Muslim nations engaged in civil wars tend to spark terrorism against the occupiers, to encourage behavior contrary to liberal values and to fail outright, usually at great expense. They might point out that failed states abound throughout history, and yet few have produced terrorists targeting the U.S.. They might note that even where such terrorists do appear, we hardly need to reinvent the local government: We can target our enemies with allies on the ground or, if that fails, by gathering allies’ intelligence for airstrikes or raids.

For seven years we have been demonstrating that we cannot re-engineer foreign societies at a reasonable cost. Not surprisingly, during that time, cost was no object. Now that it is, we may finally sort out our needs from our wants, and divorce counterterrorism from state-building.