PEARL HARBOR — The U.S. military plans to gather three aircraft carriers off Guam this summer for exercises that will mark the first time since the Vietnam War that so many of the ships have operated in the Pacific Ocean together.

Air Force planes and Marines will also participate in the maneuvers scheduled for June.

Adm. Gary Roughead, U.S. Pacific Fleet commander, said the exercises will offer the Navy a unique opportunity to have three fighter wings practice together. They would also let the military test how well the aircraft carriers, the Air Force and the Marines share information, he said.

Capt. Matt Brown, a spokes-man for the U.S. Pacific Fleet, said the Navy had to go back to records of the Vietnam War to find three aircraft carriers operating together in the Pacific.

Roughead said Guam's central location makes the waters off the U.S. territory the best place for the ships, planes and troops to rendezvous without spending too much time in transit.

The size of the exercises will likely grab the attention of other nations.

Ralph Cossa, president of the Pacific Forum Center for Strategic and International Studies in Ho-nolulu, said significant exercises inevitably send political messages even though they are designed primarily to help troops hone their skills.

Cossa said the June maneuvers would demonstrate to Iran and North Korea that, despite the focus on the war in Iraq, the U.S. would have resources at its disposal in the event of a military confrontation with either country over its respective nuclear programs.

Cossa said it was unlikely that the U.S. aims to send China a message with the exercises even though it might be a popular interpretation of U.S. intentions.

"I would think today that the U.S. is certainly more concerned that the Iranians and the North Koreans know that we still have the ability to put together a formidable amount of firepower," Cossa said. "The Chinese already know that. And the Chinese aren't doing anything that would require us to send them that message."

The exercises come just months after the Pentagon's Quadrennial Defense Review said the Navy would heighten its presence in the Pacific to keep up with the growth of trade and transport in the region.

The Navy plans to base most of its nuclear-powered attack submarines in the Pacific by 2010. It also intends to have six — or half — of its aircraft carriers available for operations in the Pacific at any given time.