Washington ? Prewar forecasts that failed to account for a lengthy and bloody insurgency have left the military struggling to provide all the equipment needed to do battle in Iraq, defense officials said Monday.

The Army has made substantial progress in equipping soldiers since last December, when the top ground commander in Iraq, Lt. Gen. Ricardo Sanchez, complained of shortages to his superiors. But post-invasion projections that did not account for persistent assaults on U.S. troops have left supply strategists straining to catch up, even as they contend with equipping the troops over increasingly perilous Iraqi roads.

The insurgency revealed gaps in the effort to equip the troops, said a senior official who oversees the effort to supply the Army.

“We had communications problems, we had infrastructure problems in the theater,” said Gary Motsek, director of support operations for the Army Materiel Command at Fort Belvoir, Va. “The war clearly went on longer than expected, based upon what we thought we had to do. And the nature of the war changed.”

Body and vehicle armor were the most glaring shortages. While every American soldier in Iraq has had body armor since January, and the backlog on Humvees needing repair has gone from hundreds to zero since last winter, many vehicles still lack armor.

And heavy use has led to a persistent shortage of critical parts for helicopters, Humvees and tanks, according to a forthcoming Department of Defense study.

“The requirements issued from the theater have changed many, many times,” said one Army official who deals with issues involving troop readiness. “Eighteen months ago, we were supposed to be gone from Iraq by now. So how much do you buy?”

The supply problems were highlighted last week after an Army Reserve unit in Iraq disobeyed a direct order to deliver food, fuel and other supplies. The soldiers of the 343rd Quartermaster Company, from South Carolina, said they believed that the poor condition of their fuel trucks and the lack of armored vehicles to escort them meant they were being asked to perform a “suicide mission,” according to the troops’ family members. The Army has begun an investigation.

Army officials say they are improving their ability to stock parts and equipment, boosted the readiness rates of tanks and helicopters and shortened waits for new supplies. Yet, in some categories, they still fall short of their own goals.

The time it takes to get critical equipment to the battleground dropped from a peak of 53 days last December to 24 days last month. But the Army is still short of its goal — 14 days — largely because insurgents have made attacking supply convoys with roadside bombs and rocket-propelled grenades a central part of their strategy.

In response, the Army is doing more repairs in Iraq and storing parts in Kuwait. To minimize the number of troops and contractors forced to make the perilous 800-mile trek from Kuwait, equipment bound for central and northern Iraq is being airlifted to a distribution center in Balad, about an hour’s drive north of Baghdad. Because they consider the roads unsafe, the Marines have begun airdropping their equipment directly to their destinations in central Iraq.