WASHINGTON — Soldiers will slide down rock-strewn hillsides in Hawai'i to test the seats of new prototype uniform pants to replace those that have come apart at the crotch during fighting in the rugged terrain of Afghanistan, Army officials say.

"These guys are actually sliding down the mountainsides on their butts," said Fred Coppola, an Army official working on the problem. "In a lot of cases, it was too mountainous, too rugged, too steep to try to walk down."

The new uniforms could reach soldiers in Afghanistan as early as this spring, traditionally the time when Taliban insurgents have mounted offensives. Defense Secretary Robert Gates recently announced the Pentagon is sending 3,200 Marines to Afghanistan this spring. They will join about 26,000 soldiers already there.

Finding the proper solution to the uniform problem has been difficult. In one case, researchers sprayed the pants with the same type of rubbery material used to protect the beds of pickups. That effort failed because the material was flammable, Coppola said. "It went up like a torch."

A flame-resistant substitute was found, and it now bolsters the bottom of one uniform to be tested.

Another contender is a patch of tough fabric sewn onto the seat and inseam. Finding the right balance between strength and comfort isn't easy, Coppola said.

"I could put steel plates in the butts, but that's not going to be very comfortable," he said.

Hundreds of the uniforms will be shipped this month to soldiers in 25th Infantry Division in Hawai'i.

The soldiers will "scooch around on their butts" to test them out, Coppola said.

"They have the lava rocks, and the lava formations in certain parts of Hawai'i that we can use to replicate the same severity of the Afghan theater," he said.

If a uniform stands up to the abuse, it could fielded in as little as three months, Coppola said.

Brig. Gen. Mark Brown, who commands the Army's Program Executive Office Soldier, which fields gear for soldiers, learned of the problem with the pants during a visit to Afghanistan in August.