Kenmore gas oven Bake Burner lights for 20 seconds then shuts off

Kenmore gas oven Bake Burner lights for 20 seconds then shuts off I have a Kenmore Gas Oven model 790.36933900. The stove top burners work just fine, but the baking burner does not stay lit. The igniter glows and lights the burner, and the burner runs for 20 - 30 seconds and then turns off. After turning off the burner will re-light after about 20 seconds, then turn off again. The baking burner continues turning on and off every 20 seconds (or so) and the igniter remains glowing the entire time.