Yes, it sounds like the switch. The way it works is when the motor is off, the contacts close and the starter winding is connected to the power. As the motor spins up, the switch moves outwards to the centrifugal force and opens the switch disengaging the starter winding.

So, take a look at the switch and in it's off closed position there should be some contacts that are closed. Those are the ones that should be cleaned. However, it could be a bad spring too which is not fully closing the switch when the motor is off so take a look at that too.