Many military experts believe that reviving some sort of military draft is extremely unlikely, even impossible -- but not all of them.

The issue has taken on urgency because of the dynamics of the presidential campaign, with Democratic operatives using the prospect of a draft to drive the youth vote, and the Democratic nominee himself raising the possibility on the campaign trail.

Neither presidential candidate supports resuming conscription. President Bush, responding to John F. Kerry's assertion that there is a "great potential" that a reelected Bush could restart a draft, insists that it will not happen. And Defense Secretary Donald H. Rumsfeld said last week: "The truth is, we do not need a draft. We're not going to have a draft."

Overwhelmingly, military insiders agree with both of Rumsfeld's points. "Very simply and strongly, I do not foresee a need nor a desire for a draft," retired Army Lt. Gen. Joseph K. Kellogg Jr. said in a comment typical of those heard across the armed forces. "The all-volunteer military is a thing of true magnificence and should not, and need not, be changed." Resuming conscription, he added, has become one of the lethal "third rails" in American politics, akin to fiddling with Social Security.

But a small minority of defense specialists say that, given the strains placed on the U.S. military over the past three years, they can imagine scenarios in which a new conflict would require significant numbers of new troops -- and in which the draft would be reinstituted.

Oddly, the debate comes as the all-volunteer force experiences the first sustained ground combat in its history -- and just after the last draftee has left the Army. On July 29, Sgt. Maj. Archie Turner, who was conscripted in January 1973, retired from the Defense Logistics Agency after more than 31 years of service.

Army Maj. Donald Vandergriff, author of two influential books on military personnel policy, said that if current strains on the armed forces continue, especially the need to keep 130,000 U.S. troops in Iraq, he could see the need for a draft.

"If the force is stretched and the same people are always rotating with little breaks in between, they become worn out, tired, start becoming bitter, start making mistakes," he said in an e-mail interview. The Army's recent moves to restructure itself to have more deployable brigades, and to keep soldiers in one unit longer, are steps that promise to lessen that strain, he said.

Even so, Vandergriff said: "We either have to come up with a plan that details how we are going to sustain the long-term effectiveness of our force for a decades-long war that says we can continue to do it with the volunteer force, or have to look at other alternatives like the draft."

For the past 30 years, the Army and the other services have filled their ranks with volunteers, lately recruiting about 190,000 enlistees annually. Today there are 1.4 million people in the active-duty force and 865,000 in the Guard and reserve components. Rumsfeld is fond of pointing out that every one of them asked to be there -- while Kerry likes to note that "stop-loss" orders have prevented some from leaving, a move he has labeled a "back-door draft."

Other experts worry that trouble elsewhere, in addition to the Iraq war, could trigger a need for more troops.

An Army colonel at the Pentagon, who said he could not speak on the record about the draft without being fired, said that he does not believe a draft is politically possible, but that new crises could make it militarily necessary. "The military right now is stripped down pretty thin," he said. "If the president decided we needed to go somewhere other than Iraq, it doesn't take a mental giant to figure out that we don't have the people to do that."

Iran is mentioned frequently in such assessments. Retired Air Force Col. Sam Gardiner, an expert in targeting nuclear facilities, worries that the looming confrontation with that country over its nuclear program could result in a need to greatly expand the military. "The Iran train is bearing down on us quickly," said Gardiner, who recently conducted a private war game on how U.S. forces might attack and destroy Iranian nuclear capabilities. He estimates that "we would need four to five divisions to have a reasonable military option" to do that. The Army has 10 active-duty divisions, and most either are in Iraq, just returned from there or are preparing to go.

Likewise, retired Army Col. Lloyd Matthews, a former editor of the Army War College's Parameters magazine, said he does not foresee any possibility of a draft but also worries about the huge troop requirements that could stem from a new confrontation. "After the election, and after we obtain breathing space in Iraq, we are going to have to get serious about the nuclear situation in Iran and North Korea," he said. "If our responses in any way involve ground troops, we will have to discover new means of raising them."

Even if the military needed huge numbers of troops quickly, predicted Richard H. Kohn, a military historian at the University of North Carolina at Chapel Hill, the Pentagon first would increase recruitment with new incentives, mobilize all the reserves and take other steps, such as twisting the arms of allies to contribute troops. "At that point, the draft might be instituted, but only after every other work-around possible," Kohn said.

Many more defense experts say the United States would need a draft if its homeland comes under a clear threat. The requirement for new soldiers could then increase sharply because a large crisis in the United States would call upon the National Guard, which is being used heavily to supplement the active-duty U.S. military in Iraq and Afghanistan. There are 173,172 Guard and reserve troops now on active duty, many of them in those two countries.

Retired Army Lt. Gen. Lawson W. Magruder III said it might be possible that a draft would be needed to produce soldiers who could "serve as a backfill -- replacements -- for deployed National Guard units, if we have insufficient force to defend our own homeland from looming terrorist threats."

Likewise, a commander in the 82nd Airborne Division said he thinks it is possible that there could be a narrowly focused draft aimed only at filling the National Guard and Army Reserve but that keeps the active-duty Army an all-volunteer force.

Several national security specialists predicted that it would take more than just a vague threat to the homeland to resume the draft. "It will take something very emotion-charged to galvanize those in favor and immobilize those who would otherwise be opposed," said retired Army Col. Ralph Hallenbeck, who worked in Iraq last year as a contractor. But he noted that the attacks of Sept. 11, 2001, changed the political debate on whether to invade Saddam Hussein's Iraq.

Some experts believe that even if there is a clear and urgent need for a draft, political leaders will shy away from the idea.

"There is no question that the growing gap between the supply of U.S. ground forces and the actual and potential demands for them is approaching a condition of unacceptable strategic risk, if we are not there already," said Jeffrey Record, a professor of strategy at the Air Force's Air War College.

Record, who is also the author of "Dark Victory: America's Second War Against Iraq," a scathing critique of the Bush administration's handling of the war, said he expects other steps to be taken, more along the lines of market-oriented solutions. "I can see an expansion of the AVF [all-volunteer force] via major increases in pay and benefits," he said. "I can even see the hiring of foreign mercenaries, which is essentially what we are doing in Iraq. The Defense Department has outsourced everything else. Why not badly needed ground combat forces?"

These members of the 2nd Infantry Division were among the soldiers moved from South Korea to Iraq.Defense Secretary Donald H. Rumsfeld: "The truth is, we don't need a draft."