Don, ask the people who are designing your trusses about cutting one for the stairway. Many times, they can or will engineer a solution for you while the trusses are being built. If they are already built, they could tell you whether it is o.k. to cut one or not.
Another option is to have an engineer design an opening for you. Quite often I see trusses that have been cut to accomodate stairways and chimneys. When they are cut, there are a lot of reinforcing added to the cut truss, as well as the ones on each side. As long as the company that made the trusses or a structural engineer designs the solution, you should not have a problem.
Bob