JOINT BASE BALAD, Iraq » Early this year a “;fob in a box”; — military slang for 80 shipping containers with all the tents, showers and construction material needed to set up a remote forward operating base — was put on trucks here for the trip from one war to another.

Left over and never used in Iraq, the fob rumbled north to Turkey, east through Georgia and Azerbaijan, by ship across the Caspian Sea to Kazakhstan, then south on the old Soviet rail lines of Uzbekistan into northern Afghanistan. There — the end of a seven-nation, 2,300-mile, two-and-a-half-month odyssey — it was assembled just weeks ago as home for several hundred of the thousands of U.S. forces entering the country.

In trying to speed 30,000 reinforcements into Afghanistan while reducing U.S. forces in Iraq by 50,000, American commanders are orchestrating one of the largest movements of troops and materiel since World War II. Military officials say that transporting so many people and billions of dollars' worth of equipment, weapons, housing, fuel and food in and out of both countries between now and an August deadline is as critical and difficult as what is occurring on the battlefield.

Military officials, who called the start of the five-month logistics operation “;March Madness,”; say it is like trying to squeeze a basketball through a narrow pipe, particularly the supply route through the Khyber Pass linking Pakistan and Afghanistan.

So many convoys loaded with American supplies came under insurgent attack in Pakistan last year that the U.S. military now tags each truck with a GPS device and keeps 24-hour watch by video feed at a military base in the United States. Last year the Taliban blew up a bridge near the pass, temporarily suspending the convoys.

“;Hannibal trying to move over the Alps had a tremendous logistics burden, but it was nothing like the complexity we are dealing with now,”; said Lt. Gen. William G. Webster, the commander of the U.S. 3rd Army. He spoke at a military base in the Kuwaiti desert before a vast sandscape upon which were armored trucks that had been driven out of Iraq and were waiting to be junked, sent home or taken on to Kabul, Afghanistan.

The general is not moving elephants, but the scale and intricacy of the operation are staggering. The military says there are 3.1 million pieces of equipment in Iraq, from tanks to coffee makers, two-thirds of which are to leave the country. Of that, about half will go on to Afghanistan, where there are already severe strains on the system.

Overcrowding at Bagram Air Base, the military's main flight hub in Afghanistan, is so severe that beds are at a premium and troops are jammed into tents erected alongside runways. Cargo planes, bombers, jet fighters, helicopters and drones are stacked up in the skies, waiting to land.

All lethal supplies — weapons, armored trucks, eight-wheeled Stryker troop carriers — come in by air to avoid attacks, but everything else goes by sea and land.

The standard route from Iraq to Afghanistan is south from Baghdad and down through Kuwait, by ship through the Persian Gulf and the Strait of Hormuz to Karachi, Pakistan, then overland once again. The “;fob in a box”; went on an experimental and potentially less expensive journey through Turkey to link up with a new northern route through Central Asia, which was opened last year for supplies going to Afghanistan from Europe and the United States as an alternative to the risky trip through Pakistan.

Both routes circle Iran, by far the most direct way to get from Baghdad to Kabul, but off limits because of the country's hostile relationship with the United States. “;These are the cards that we're dealt,”; said Gen. Duncan J. McNabb, who oversees all military logistics as the leader of the U.S. Transportation Command at Scott Air Force Base, Ill.

Nonlethal supplies flowing into Afghanistan include cement, lumber, blast barriers, septic tanks and rubberized matting, all to expand space at airfields and double, to 40, the number of forward operating bases in a country that has an infrastructure closer to the 14th century than the 21st.

Gen. David Petraeus of the U.S. Central Command, in another grand historical parallel, recently called the construction under way “;the largest building boom in Afghanistan since Alexander built Kandahar,”; a reference to the conqueror of Afghanistan in the fourth century B.C.

Food shipments alone are enough to feed an army. The Defense Logistics Agency, which provides meals for 415,000 troops, contractors and American civilians each day in both wars, shipped 1.1 million frozen hamburger patties in March alone, compared with 663,000 burgers in March 2009. The agency also supplied 27 million gallons of fuel to forces in Afghanistan this month, compared with 15 million gallons a year ago.

Commanders say that their chief worry is that the equipment and supplies will not arrive in sync with the troops. Their biggest enemy, they say, is the short time between now and August, the deadline set in separate plans for each war.

Early last year, President Barack Obama and military commanders agreed on a withdrawal plan to reduce U.S. forces in Iraq to 50,000 by Aug. 31 (97,000 United States troops currently are there), with all U.S. forces out by 2011. Late last year, Obama pushed commanders to speed up the infusion of new troops into Afghanistan — military planners had originally said it would take 18 months — so that 30,000 new troops would get there by August. So far, about 6,000 of those reinforcements have arrived. Once they all get there, there will be close to 100,000 United States troops in Afghanistan.

“;There is a great sense of urgency in getting in and getting effective,”; said Vice Adm. Alan S. Thompson, the director of the Defense Logistics Agency. “;The administration is concerned about being able to show results quickly.”; There are obvious strains, he said, but “;I think it's doable.”;

McNabb, in another reference to Alexander the Great, said that when he took over the transportation command in 2008, Defense Secretary Robert Gates reminded him of the well-known words attributed to the famous conqueror: “;My logisticians are a humorless lot; they know if my campaign fails, they are the first ones I will slay.”;

Gates had his own words of advice. “;He just said, 'Hey, it's a tough job, better figure it out,' “; McNabb said.