American's armed forces are growing bigger to reduce the strains from seven years of war, but if the US is confronting an era of "persistent conflict," as some experts believe, it will need an even bigger military.

A larger military could more easily conduct military and nation-building operations around the world. But whether the American public has the appetite to pursue and pay for such a foreign-policy agenda, especially after more than five years of an unpopular war in Iraq, is far from clear.

Last week, the Army released a new manual on "stability operations" that outlines for the Army a prominent global role as a nation-builder. The service will maintain its ability to fight conventional land wars, but the manual's release signals that it expects future conflicts to look more like Iraq or Afghanistan than World War II. While Defense Secretary Robert Gates has not publicly supported expanding the force beyond what is already planned, he has said the United States must prepare for more counterinsurgency wars like the ones it is fighting now – a hint that a larger military may be necessary.

Some analysts are certain of that need.

The Army currently has about 540,000 active-duty soldiers and is expected to attain its goal of 547,000 by 2011. The Marine Corps, also tapped to expand, should top 202,000 within the next couple of years. The total American force – including active-duty, reserve, and guard – is about 2.2 million.

John Nagl, a counterinsurgency expert and a retired Army officer, says in coming years the Army should grow to 750,000 and the Marine Corps to 250,000. Demand for troops is already high, and it won't abate anytime soon even if substantial numbers of troops return from Iraq, he recently said at the Center for a New American Security, a think tank in Washington.

Meanwhile, the top US commander in Afghanistan has asked for more American troops that the US simply can't produce until more leave Iraq.

"We don't have enough brigades to fight – that is an inconvertible fact," says Mr. Nagl.

If the US is to remain a superpower in a world in which weak nations, not strong ones, are the big threats, then it must expand its forces so it won't again enter a conflict using too few troops, as it did in Iraq, say other experts. America must stay engaged in nations with weak or nonexistent governments to prevent extremism from taking root and threatening the US.

"This is not a prediction of conflicts to come, but a recognition that the potential for stabilization and reconstruction missions remains high," writes Fred Kagan, a senior fellow at the conservative American Enterprise Institute, a think tank here, in a book he cowrote called "Ground Truth." Mr. Kagan and Thomas Donnelly argue for a total force of about 2.8 million, which includes an active Army of about 800,000 and a Marine Corps of about 200,000.

"We may not want these missions, but they might be thrust upon us; and they certainly might appear to a future president as the least-bad outcome," Kagan writes.

Despite warnings against allowing the military to become the face of US foreign policy, more analysts are arguing that the resource- and manpower-rich armed forces are in the best position to fulfill any US policy pertaining to strengthening and stabilizing troubled nations.

Meanwhile, the State Department has pledged to hire 600 new foreign-service officers by next year to join the military in countries where stability operations are the main focus.

"The military is definitely out front. They are faster than [civilians] are, they are alert, and they have a lot of resources," says Daniel Serwer, a vice president at the United States Institute of Peace, which supports the Army's new manual.

The cost of all this gives some analysts pause.

Frank Hoffman, a senior fellow at the Foreign Policy Research Institute in Philadelphia, says the new manual may represent a shift for the Army, but he has yet to see major changes in the overall Army approach. "The Army is not fundamentally investing in new capabilities or creating any unique skill sets, or reducing training requirements or workload from conventional fighting," he says. It has yet to reevaluate its expensive future combat system, a cornerstone of Army modernization, he notes.

In Congress, which a few years ago was bipartisan in its support for a larger military, some are adjusting their view. Rep. Jack Murtha (D) of Pennsylvania recently argued that the cost of a bigger force is too much and could prevent the military from buying equipment.

Whatever happens, Pentagon officials know they may be charged with expanding the military beyond current growth goals.

David Chu, the Pentagon's undersecretary of defense for personnel and readiness, says meeting higher recruiting goals would require a basic shift in the way the nation views the military. He says he bristles when discussions in Washington about encouraging Americans to participate in national service programs omit the military.

"Few of those attempts, and fewer of those legislative proposals, ever mention the military," he says. If the country were to reverse that stand, "there won't be serious recruiting issues."