I have a american standard whirlpooltub that was installed by a contractor and there is no support material under the tub. It is supported by the rim only. And it is leaking. Where coulkd it be leaking from?

Many places it can leak from. The 'rim set' tub is made to be set by resting on the rim. I don't do it because I think it will flex and cause cracks. How much space under the tub? Is there a panel you can peek in?
Test the faucet by using the faucet but catch the water in buckets. Test the drain by getting water from another source besides the faucet. Then test the whirlpool pipes by filling the tub up the same way. Test the overflow too by filling up past the overflow. If no leaks yet, look for splash places on the rim.