Your symptoms point to a gas supply problem to that oven burner or a bad oven igniter. You can pull that bottom panel of the oven and the flame spreader and check that burner to see if the ports are clear.
Unplug the range
before accessing internal components. If that burner is okay, I recommend that you plug in the range and ignite that burner with the bottom oven panel removed to observe the flame. If the flame is normal but the burner shuts off while the igniter still glows, then you could have a weak igniter. The theory of operation for the ignition system is shown in the image below. If that igniter is weak and will not allow enough current to flow through the circuit to the safety gas valve, then it will need to be replaced.
You can order parts from the
website if necessary.
Be sure that you
unplug the range
before accessing and replacing internal components.
If you need more help, reply with additional details based on the above tests.
If you get to the point where you need to have a service technician examine and repair the range, you can schedule service through this link:
Sears Home Services