At Marine Corps headquarters in the shadow of the Pentagon, Col. Russell Appleton shuttles between two desks. At one, he works to cut the active-duty roster. At the other, he tracks call-ups of military reserves.

This seeming contradiction - getting smaller and bigger at the same time - points up one of the paradoxes lurking behind the scenes of the dramatic buildup in the Persian Gulf crisis.The uniformed services and their civilian overseers are orchestrating the largest U.S. military operation since Vietnam while simultaneously carrying out Congress' order to shrink the military by 80,000 people over the next 10 months.

Can it be done?

The Pentagon says "yes." But there are growing indications that military leaders may ask Congress to set aside the troop-cut goals.

Appleton, head of manpower policy and planning for the Marines, may have to tuck away his "force reduction" files because, as he said in a recent interview, "putting 200,000-plus soldiers, sailors, marines and airmen on the other side of the world . . . isn't business as usual."

Even more unusual is the challenge of adding yet another 200,000 troops as reinforcements for the original deployment, as ordered Nov. 8 by President Bush to get Iraq out of Kuwait.

When the full contingency of perhaps 430,000 personnel is in place, nearly one-quarter of the entire American armed forces will be committed - more troops than the United States had in Europe at any time during the Cold War.

Just a few months ago, Congress put the Pentagon on a path toward reducing troops by up to 500,000 over the next five years - part of the now-aborted drive to gain a quick "peace dividend" from the collapse of communism.

Even in the seemingly unlikely event that the gulf crisis is resolved peacefully and soon, it may force Congress and the Bush administration to take a new look at how to restructure and reduce U.S. forces in the post-Cold War era.

The problem is seen most clearly in the colliding paths of reserve and active duty forces.

The military says it must cut officers and enlisted personnel to meet the force-reduction targets set by Congress, yet it can't prepare for a possible war against Iraq without adding more than 100,000 reservists to the active duty force.

The reserves provide vital skills not available in the active-duty force, such as certain medical, transport, water purification and construction services.

Somewhere in the sands of Saudi Arabia the paradox takes on real-life meaning.

"The fact is there's a reserve colonel standing out there next to a regular colonel (facing a forced retirement), and it can become a very, very emotional issue," Appleton said.

The Army, which must absorb about half the 80,000 personnel cuts for the total U.S. armed forces by Sept. 30, has found a temporary solution to the conflicting demands presented by Congress and the gulf crisis.

On Nov. 23, it froze all active-duty personnel in their positions. In effect it acknowledged - though not in so many words - that it could not continue cutting the force while putting roughly 200,000 Army personnel in Saudi Arabia.

"If we go to hostilities then all bets are off because you then have casualties that you have to replace," Appleton said. "It changes the calculus completely."

Yet even now the Marine Corps, while officially preventing some of its personnel deployed for Desert Shield from leaving the service, is using retirement boards to decide which 100-plus active duty officers will be forced out of uniform.

The Air Force plans to convene a retirement board this month to force as many as 750 colonels and lieutenant colonels out of uniform.

The Army decision to freeze its force, made with the approval of Defense Secretary Dick Cheney, meant that about 5,500 personnel per month who otherwise would have chosen to leave the Army will be kept in uniform indefinitely, according to an Army planner who spoke on condition of anonymity.