Seeping seawater has forced the U.S. military's most powerful missile defense radar to abort a voyage from Hawai'i to Alaska, delaying the $815 million device's arrival at its home port.

The giant, white bulbous radar dome — looking like a King Kong-sized golf ball — returned to Pearl Harbor mounted on its converted floating oil drilling platform four days after leaving O'ahu on March 31.

"It made more sense to come back into Pearl Harbor to do the repairs than to try to do them out on the open water," said Pam Rogers, a spokeswoman for the Missile Defense Agency.

"It was close enough to Pearl that they could return fairly easily."

Repairs won't be completed until this week at the earliest, Rogers said.

The floating radar is designed to be capable of identifying objects as small as a baseball from thousands of miles away, giving the U.S. military an advanced tool to help it spot and intercept incoming enemy missiles.

It is seaborne to give the military the flexibility to send the radar where it would be most needed.

The agency said the floating structure suffered damage when water leaked through its ballast piping, affecting its ability to partially submerge and re-emerge from the water.

A few communication antennas also suffered minor damage during transport, but the radar itself was not affected, Rogers said.

The Missile Defense Agency was still tallying the cost of the damage, but "it should be minimal," she added.

The radar arrived in Pearl Harbor in January on board the MV Blue Marlin, but it was attempting to reach its new base in Adak, Alaska, on its own power. The suspended trip marked the first time the vessel cruised on its own since it underwent test trials in the Gulf of Mexico.

The Project on Government Oversight, a Washington D.C.-based watchdog group, criticized the delay in the radar's deployment.

"The X-Band Radar was supposed to be ready by the end of 2005, and here we are nearly midway through 2006 and no one can even get it to its home port in Alaska," said Nick Schwellenbach, project investigator.

He said the setback was another slip for a missile defense program that costs taxpayers billions of dollars a year.