If the shoe fits, program it.

Puma USA said today it has managed to combine two of the nation's fads -- running and computers -- in one shoe. Beginning in spring 1986, Puma will market a running shoe with a built-in electronic device that can be plugged into your handy home computer and can tell you how far you ran, how fast and how many calories you used, and then can tell you how faithfully you have kept to your running program.

"The most important aspect of this shoe is that you can personalize your own running style into the computer," boasted Dr. Peter R. Cavanagh, Puma's adviser on sports science.

Puma's step into the race of computer technology follows last month's announcement by Adidas of its new Micro Pacer. The Adidas shoe, which is expected to cost about $125, will use state-of-the-art wiring and a computer chip to register average speed, length of stride and calories used. But it doesn't require a personal computer.

Puma think it's taking a leap forward. Its RS Computer Shoe and accompanying software package, compatible with the Apple II and Commodore 64, will retail for $200. The top-quality outer shoe -- in case it wears out -- can be purchased, minus the electronic device, for $95.

Weighing only 30 grams, this self-contained data-recording device is tucked into a wedge-like unit in the heel of the left shoe. Information can be accessed immediately or stored indefinitely as long as the shoe is not turned off.

After a run, the shoe is "plugged in" to a computer with an 18-inch cable, and using individualized data preprogrammed on a floppy disk, the exact distance run and the amount of calories used are calculated.

Daily, monthly or yearly performance records are displayed in colorful graphs, and a runner can even set goals that can be compared graphically to the actual distance run.

And for the forgetful runner, the shoe can be programmed to beep when a specific distance is achieved.