WASHINGTON — Concerned that U.S. troops are already saddled with too much heavy gear, military officials will not require them to wear improved body armor until manufacturers cut the weight of the new protective plates.

The Army plans to buy 120,000 sets of the advanced bullet-blocking plates this year. This initial purchase of the plates, known as "XSAPI," will be stocked in Kuwait and be available if commanders need them, service officials said at a congressional hearing Wed-nesday.

U.S. soldiers currently use "ESAPI" body armor plates, but their quality was called into question last week in an audit by the Defense Department inspector general's office. The Army disputed the conclusion, calling ESAPI the best body armor available.

The body armor used by most American forces consists of a vest with a series of inserts that protect most of the upper body from armor-piercing rounds. The specially hardened ceramic plates are the largest of the inserts; one is placed in the front of the vest and another in the back.

But making the roughly 6-pound XSAPI any lighter is harder than it sounds. The plate has to be thick enough to defeat new and more potent bullets finding their way onto the battlefield, says Joel Moskowitz of Ceradyne in Costa Mesa, Calif., one of the companies making XSAPI.

"A certain amount of thickness is required," Moskowitz said Wednesday in an interview. "You just need that to stop that first hit."

Contracts potentially worth $6 billion for XSAPI and ESAPI plates were awarded in October to Ceradyne, BAE Systems of Phoenix, and The Protective Group of Miami Lakes, Fla. The work was put on hold after BAE filed a protest over the manufacturing schedule.

Overall, the military could acquire up to 1 million sets of XSAPI plates.

ESAPI plates range in size from extra small to extra large and weigh on average 5 1/2 pounds each. XSAPI plates come in the same sizes and weigh about half a pound more.

An extra pound for a pair of plates may not seem overly burdensome. But when added to the combat loads the troops already carry — backpack, combat rifle, ammunition, helmet — it creates more strain, particularly in harsh environments like Afghanistan, the Army says. Troops must often track insurgents on foot and every pound counts.

"Over time, the body armor, it does wear on your body," said Army Staff Sgt. Fred Rowe, who has done two combat tours in Iraq. "I couldn't imagine doing what I did, carrying what I carried, in Afghanistan."