WILLIAM L. DeANDREA's Killed in the Ratings is a mystery as topical as the overnight Nielsen ratings. The title does not refer to CBS or NBC in the current television season of ABC successes. The first victim (more to follow after a break for detection) is a computer programmer for ARGUS, an audience measurement system. An Argus rating from a 1200-home sample can make or kill a television show, influence the eating, sleeping and bladder habits of millions of Americans watching television, and decide how millions upon millions of advertising dollars are allocated.

What makes Killed in the Ratings (Harcourt Brace Jovanovich, $7.95) such an engaging mystery novel is background rather than plot, which is adequate but not inspired. Author William L. DeAndrea, who couldn't find a job in broadcasting after college and decided instead to write a mystery about the business, gives us a 21-inch picture of the machinations of the TV world - the ruthless rivalry between networks, the jockeying for executive position, the frantic programming that turns on a percentage point in ratings rather than the merits of a show.

The story is told by Matt Cobb, a breezy, brash young troubleshooter in the network's special projects department, whose job is to handle messy matters like a kleptomaniac star or alcoholic producer. He longs to be back in the news department, where he was an associate producer like Mary Tyler Moore. Instead, he finds himself involved in a murder that raises suspicions why Harbor Heights , which promised to be a surefire winner as a new television series, bombed in the ratings.

DeAndrea has great fund using quotations from TV shows as chapter lead-ins. Example from Chapter 3: "Now let's see what terrific prize is waiting for you behind that door!" - Monty Hall on "Let's Make a Deal." For Matt Cobb, it's a body with a knife stuck in the middle of its back.