Dieters using a computer that congratulated them when they did well and told them how to improve when they did poorly lost more than twice as much weight as people who dieted the old-fashioned way, Stanford University scientists report.

The microcomputer, small enough to be carried around all day, was used to record food intake and activity. Six dieters regularly entered food codes numbers and portion sizes, in addition to kind and amount of exercise, on the computer's keyboard.

Six other dieters were asked to keep track of the same data with paper and pencil.

When a computer user met goals for exercise or food intake, the computer responded with a line of praise on a small screen, such as: "Fantastic (subject's name), you have self-control!"

This reinforcement was key to the computer dieters' success, Stanford's W. Stewart Agras and his colleagues wrote in the Journal of Consulting and Clinical Psychology. The computer provides a means of immediate feedback to change behavior; without it, they wrote, feedback "is often delayed until the next meeting with the therapist . . ."

On the average, the computer dieters lost 8.1 pounds in eight weeks, compared with 3.3 pounds for those who did not use the computer.

It remains to be determined, the researchers wrote, how 1274