Up to 3,000 Olympics slides which were to make up the bulk of photographs in the next issue of Sports Illustrated magazine were stolen Thursday, officials said. ``It's the biggest athletic event of the year and this is our picture record of it. They're our life's blood,'' said Joe Marshall, director of photography for the magazine. The pictures were stolen from the front seat of a locked, parked van enroute Thursday to the magazine's offices in midtown Manhattan, said Louis Slovinsky, director of public affairs for Time Inc. Marshall said pictures often are hand delivered by staff members but were sent via an air freight company as the games continued in South Korea. The stolen slides, chosen from 50,000 pictures shot by nine magazine photographers on Monday, Tuesday and Wednesday, included pictures of shamed 100-meter sprinter Ben Johnson, Greg Louganis's second gold medal in diving and the U.S.-Soviet basketball game, Marshall said. Slovinsky said the magazine would pay an unspecified reward and ask no questions if the pictures were returned. ``These are extremely valuable pictures for Sports Illustrated, but they are of no value to anybody else,'' Slovinsky said. The slides are each clearly marked as belonging to Sports Illustrated and being from the 1988 Summer Olympics, he said. Slovinsky said photographs belonging to the Black Star Publishing Co. Inc., a photo agency, also were stolen from the truck.