WASHINGTON (AP) - Army planes with high-tech surveillance equipment were preparing Wednesday to take to the skies around the nation's capital to help track a sniper who has eluded law enforcement officials for two weeks.

The planes were being flown to the region and were expected to join the hunt within days, a defense official said Wednesday, speaking on condition of anonymity.

Authorities called in the military Tuesday to help solve the baffling case that has left nine people dead and terrorized the capital area, leaving people afraid to go out of their homes. Defense Secretary Donald H. Rumsfeld on Tuesday evening agreed to an FBI request for the help, approving use of the Army's Airborne Reconnaissance Low plane, which has surveillance capabilities beyond those of local police forces, defense officials said.

The plan calls for military pilots to fly reconnaissance flights accompanied by federal agents, who would relay any collected information to authorities on the ground, a senior defense official said, speaking on condition of anonymity. A main objective is to improve communications among investigators.

The military planes join a chase that already is using officers from more than a dozen law enforcement agencies, along with dragnets, roadblocks, bloodhounds, helicopters and other tactics. Among important features of the four-engine plane are that it provides high-resolution imagery and night vision and looks like a small commercial plane, making it easier to blend in with local air traffic and avoid detection.

The Pentagon help will be given in a way meant to comply with the Posse Comitatus Act _ a 19th century law that restricts the military's involvement in domestic law enforcement, said Pentagon spokesman Lt. Cmdr Jeff Davis. That means the military will not be involved in action on the ground, will relay data to law enforcement and not decide on its own what targets to watch, officials said.

The move is highly unusual but not unheard of.