Heavy layers of body armor, a proven lifesaver of U.S. troops, also may be an impediment to winning the fight in Afghanistan. where 17,000 additional American forces are being sent to quell rising violence.

Weighing as much as 34 pounds each, the protective vests hinder American forces hunting down more agile insurgents who use the country''s rugged peaks and valleys to their advantage, according to military officials.

The proper balance between troop safety and mobility will be examined this week during a series of oversight hearings by the House Appropriations defense subcommittee. Beginning Tuesday, senior Army and Marine Corps leaders are scheduled to testify on a wide range of subjects, including force protection, readiness levels and ergonomic injuries.

When body armor is added to the assault rifles, ammunition, water and other essential gear troops are required to carry, they can be lugging as much as 80 pounds into combat. Besides moving more slowly, overburdened troops tire more quickly and are prone to orthopedic injuries that can take them out of action, the officials say.

But convincing a war-weary public of a less-is-more approach won''t be easy, they acknowledge. If a commander decides the gear shouldn''t be used for a particular mission and a service member is killed, there could be a backlash, said Jean Malone, deputy director of experiment plans at the Marine Corps Warfighting Lab in Quantico, Va.

"We''ve got to have the internal fortitude to come back and say: ''We have the data. We made the right decision. We can''t guarantee you that nobody will die in this war,''" he said.