A Twentynine Palms Marine pleaded not guilty in an Indio courtroom yesterday to trying to bring live military ordnance onto a plane in Palm Springs in March. Steven Vella, 21, was arrested March 4 as he tried to board his flight to New York. Authorities had discovered inside his luggage two live smoke grenades, a dummy hand grenade, and inert mortar body shell, and three ground burst simulators. Steven Vella is a Marine stationed in Twentynine Palms with Headquarters Battalion, 7th Marine Regiment.