WASHINGTON  The Army has promised to lighten the soldier’s load, and nowhere more urgently than in eastern Afghanistan, where the unforgiving terrain tests the stamina of troops whose weapons, body armor, rucksacks and survival gear can weigh 130 pounds.

But an experiment to shave up to 20 pounds off a soldier’s burden  much of it by reducing the bulletproof plates that protect the chest and back  has stalled, leaving $3 million in new, lightweight equipment sitting in a warehouse in the United States instead of being sent to the war zone where it was to have been tried out by a battalion-size group of 500 soldiers. The delay offers a new window into how Army rules have slowed the deployment of specialized gear that small units are seeking for harsh combat environments.

The new lightweight bulletproof plates, part of what is known as a Modular Body Armor Vest, are already in use by the military’s Special Operations Command, which includes the Army’s elite light-infantry troops, the Rangers.

A team of Army experts went to eastern Afghanistan in early March expecting to begin trial runs of the gear for regular Army soldiers, including a company assigned to the remote Korangal Valley, a harsh and primitive area of eastern Afghanistan where the insurgency has proved especially resilient, and where soldiers regularly set off on multiple-day patrols that require them to hike up and down steep hills and valleys.