WASHINGTON — The National Guard's deployment to the Gulf Coast, which began amid worries about overburdening citizen soldiers already spread from Mississippi to the Middle East, has instead underscored a different — and perhaps greater — challenge: a chronic shortage of the equipment that Guard members need.

Though the head of the National Guard says he had more than enough troops, Lt. Gen. Steven Blum acknowledges that trucks, bulldozers and communications equipment "all were in short supply for Katrina." He met the needs of the recovery by shifting resources among states, but the strain hints at a broader concern about the military's mechanical workhorses — both here and abroad.

Much of the Guard's equipment is in Iraq, and the war there has battered the helicopters and Humvees of every service, wearing them out five times faster than normal, by some estimates. The Pentagon says it will take at least two years to return the force to full strength after the war.

In the meantime, though, the Guard is left to do its homeland mission with the leftovers. It has long been at the bottom of the military food chain, receiving fewer Army hand-me-downs than it needs because it has typically been a reserve — the last to fight. Yet now, with the Guard being used as a front-line force in Iraq, and with President Bush pushing for a larger military role in disaster relief at home, the Guard's lack of material is a primary matter of American security.

"I don't have all the equipment I need for 300,000 soldiers," Blum says. "Equipment is my challenge now."

In Iraq, it is forcing troops to use every bit of their ingenuity — performing maintenance that would normally be done in stateside industrial depots, and jerry-rigging vehicles to withstand the insurgency and the sun. Along the Gulf Coast, the situation has forced officials to scour Guard units across the country, taking their equipment and sending it to hurricane-damaged areas.

For a force that is often made to do more with less, the interstate sharing of materiel, called cross-leveling, is a normal practice. The war in Iraq, however, has forced the National Guard to scramble even more than usual. When Guard units rotate out of Iraq, many are being told to leave their best equipment behind. In total, the National Guard estimates that it has only 34 percent of its equipment available in the United States.

Blum says communications systems in particular were scarce during the Katrina rescue operation, but he adds that he could have used more of almost everything. He filled those gaps through cross-leveling, but "that's a stop-gap solution" that pushed the Guard to the edge of its capabilities.

For decades, there has been little need for the Pentagon to invest time and resources in the Guard. It was used only as a reserve, which meant its needs were secondary. But with the Defense Department now using the Guard as an operational force, "that model doesn't fit the current reality," Blum says.

Congress, too, is aware of the Guard's changing mission. Sens. Christopher Bond, R-Mo., and Patrick Leahy, D-Vt., asked the president last week to press for $1.3 billion in spending on new National Guard equipment. "The National Guard has deployed many of its resources overseas, consequently there are insufficient reserves of equipment available to respond to future disasters," they wrote.

Across the armed forces, the war is straining equipment. The Pentagon had not originally expected such a prolonged insurgency, so soldiers have used vehicles such as Humvees in ways they hadn't expected — weighing them down with makeshift armor, for example, which puts excess wear on other parts.

Then there's the desert, which blows sand into every crank and gear and fries vehicles in a furnace of 120-degree heat.

"They're wearing out because the environment is so harsh," says Christine Wormuth, an analyst at the Center for Strategic and International Studies.

One analysis by the Congressional Budget Office suggests that once the war ends, it will take $20 billion to return military equipment to prewar condition.