WASHINGTON - The war in Iraq marks the first time in modern history that the United States has fought an extended conflict with an all-volunteer military.

The strain of fighting nearly four years in a two-front war has put unprecedented stress on the Army and the Marine Corps, which have borne the brunt of the fighting. It also has raised serious questions about whether an all-volunteer force can be maintained over the long term or whether a draft is worth looking at.

Even if troops were to pull out of Iraq tomorrow, the United States faces a war of unknown duration against al-Qaeda in Afghanistan and elsewhere. Other threats include Iran and North Korea.

The Iraq Study Group warned in its report last month that the war in Iraq has put the country in a bind.

"An extraordinary amount of sacrifice has been asked of our men and women in uniform, and of their families," the group wrote. "The American military has little reserve force to call on if it needs ground forces to respond to other crises around the world."

"I think America is on a collision course with itself because America has worldwide obligations," said Frank Schaeffer, co-author of "AWOL: The Unexcused Absence of America's Upper Classes From Military Service -- and How It Hurts Our Country."

"All it's going to take is one more conflict or one more world crisis," Schaeffer said, "and we would be very soon facing the fact that no matter what our position on these issues is, we're going to be facing a simple choice of act or don't act. And if we do, then we're going to have to have alternatives."

At least one lawmaker has proposed a radical alternative. Rep. Charles Rangel, D-N.Y., wants to reinstate the draft.

Service requirement

Rangel's proposal would require all U.S. residents ages 18 to 42 to perform two years of national service, either in the military or as civilians working in ports or hospitals or filling other public service roles. The only people exempted would be high school students up to age 20, conscientious objectors and those too unhealthy to serve.

Rangel, an Army veteran who received a Bronze Star in the Korean War, opposes the Iraq war and has put forth a draft bill every year since 2002. Critics accuse him of political grandstanding.

Some fellow lawmakers find his basic argument compelling: If the war in Iraq is the national security threat the Bush administration says it is, shouldn't all Americans be asked to do their part to defend the country?

"I think it's a legitimate question to ask," said Rep. Sanford D. Bishop Jr., D-Ga. "I don't personally believe the country is ready for a draft. But I believe that if they felt a serious enough threat, all able-bodied Americans would probably want to support our national security in whatever ways they could."

Asked recently why he has never asked Americans to make sacrifices for the war, the president said people have sacrificed in other ways.

"I think a lot of people are in this fight," Bush said in an interview Jan. 16 with PBS news anchor Jim Lehrer. "I mean, they sacrifice peace of mind when they see the terrible images of violence on TV every night."

The president said he had considered a draft but rejected it. "I think the volunteer army is working, and we've got to keep it strong," he said.

Alternatives to draft

The United States hasn't had a military draft since 1973, when Congress eliminated conscription as the Vietnam War drew to a close.

For most of its history, the United States has been without a draft. The North and the South conscripted forces during the Civil War. There was a draft during World War I and again during World War II. The most recent draft lasted from 1948 to 1973.

Many military officers, lawmakers and analysts oppose bringing back conscription, saying it would ruin the professionalism and quality that the all-volunteer force has built over the past 34 years.

"The nature of decentralized tactics today demands a level of professional experience and competence far above what it was 30 and 40 years ago," said Rep. Geoff Davis, R-Ky., a former Army officer and West Point graduate who serves on the House Armed Services Committee.

Davis, who wrote an opinion piece last month that ripped Rangel's proposal to revive the draft, said he thought that the Army could easily recruit to the level that the Bush administration wanted "with the right kind of expansion plan."

The Bush administration recognizes that there is a problem and has promised to add 92,000 service members to the Army and the Marine Corps over the next five years.

But that means Army recruiters will have to sign up an additional 7,000 men and women every year when they already are struggling and standards have been dropped to meet the current quotas.

Gen. Peter J. Schoomaker, the Army's chief of staff, has suggested that part of the answer is increasing the incentives to enlist. The Army already offers as much as $40,000 to recruits, however, and personnel costs are taking a larger chunk of the defense budget every year.

In the meantime, Defense Secretary Robert Gates has outlined plans to call up the National Guard and Reserves more frequently. But the more the military relies on its citizen-soldiers to fight the war, the less attractive the Reserves become to those who don't want full-time military careers.

There are concerns that overusing the Guard and Reserves could strain those forces as badly as the active-duty ranks.

"This is clearly not a risk-free set of solutions," said Christine E. Wormuth, a senior fellow at the Center for Strategic and International Studies, a national security research center, and a former Pentagon official who has written extensively about the National Guard and Reserves.

Managing a draft

The Pentagon estimates that it would cost about $4 billion more a year to reinstate the draft. New facilities would have to be built to train and house the large numbers of inductees who would be brought into uniform each year.

The Census Bureau estimates that there are 30 million people ages 18 to 25 in the United States.

About 4 million men and women reach military age each year, but the military needs only a small fraction of that number. That is a fact that those who argue for a return to the draft tend to overlook, said Bernard D. Rostker, the author of "I Want You: The Evolution of the All-Volunteer Force."

"The fundamental question -- which dogged us in the '60s and would dog us again if we return to conscription -- is who serves when not all serve?" said Rostker, who has studied military personnel issues for more than three decades and served as a top Pentagon official in the Clinton administration.

Draft proponents say that those whom the military doesn't need could work in homeland security guarding airports, seaports and borders, or could work in understaffed hospitals or schools.