A Navy anti-submarine helicopter crashed while preparing to land on a frigate in the North Arabian Sea and its three crewmen were presumed dead, officials announced Friday. The SH-2F helicopter was returning to the USS Barbey at the end of a dawn flight and crashed on approach, said Ken Mitchell, spokesman for North Island Naval Air Station. The Barbey is based at San Diego. The crash occurred about 7 p.m. PST Thursday, Mitchell said. Lost and presumed dead were Lt. Cmdr. Gerald C. Pelz, 37, of Coronado, Calif., Lt. j.g. Gerald T. Ramsdell, age unknown, of Ridgewood, N.J., and the anti-submarine warfare operator, Petty Officer 3rd Class William E. Martinie, 24, of Peoria, Ill. Helicopters from the aircraft carrier USS Nimitz, 70 miles away, and boats from the Barbey and USS California unsuccessfully searched for survivors. The craft was part of Helicopter Anti-Submarine Squadron Light 33.