Running over newly seeded grass with a tractor is a bad idea and should be avoided.

I agree with kidhorn. You don't want to run any kind of machinery over a newly seeded area. Perhaps you could keep the machinery stored under a tarp or some other covering elsewhere?

Running a tractor over any ground will surely compact it over time. Running it over a newly seeded lawn is a great way to kill the grass, compact the soil and never have to bother with grass there again.

If the tractor has to get to point 'A' and not stay there, then why not put down some two by sixes as a track for the wheels, then pick them up behind the tractor. This spreads the load, the weight, over a wider area. The grass should respond well.