Mattel page and Missile Attack.

[Neil UK]

The Mattel page states

"Mattel started making electronic games in 1976 with the handheld Missile Attack game (which lived only a short time), and soon followed by Football and Auto Race."

but the Missile Attack page says

"Missile Attack was released in 1977, (I had originally been told that this was the first one that they released, but it actually followed Auto Race and Football, this has been confirmed both by the programmer of Auto Race and Football (Mark Lesser) and one of the project engineers of the first games (Gary Cummings)). "

so I'm guessing that the latter is correct.

Neil.