Can you replace front tires only on a all time 4 wheel drive quad trac Jeep Cherokee Will a difference in diameter between front and rear tires damage the transfer case and or differential?

Can you as in are you able to? Yes if a tire shop will take the risk of doing it. Is it recommended? NO. I have personally seen this cause transfer case issues in Chrysler vehicles. The rule most will follow on this is that there can not be any more than 3/32" tread depth difference between any two tires on a four wheel drive vehicle. Especially an all time four wheel drive. On most lock in, lock out, 4wd vehicles it could be pulled off simply by not using the four wheel drive until you replace the other 2 tires.

Its certainly not recommended but it can be done with minimal risk as your not changing the diameter of the tires being turned with force from the transfer case. However, when you're always in 4wd you ARE changing the rates at which each differential is turning, not signifacantly, but enough for a weak drive train (which Chrysler is known for) to take issue, and cause you very expensive drive train repairs.

My best advice, bite the bullett and get 4. If you absolutely can't and must have new tires, plan to purchase the other two tires ASAP after replacing the front two. Just don't leave two different diameter tires on an AWD vehicle for an extended time.