Is it possible to perform a step climb and/or enter this on the fmc in the a310 on msfs?

Yes, you can step climb the A310. The PROG page will tell you the OPT and MAX FL. However, if you are thinking of entering all step climb FL like you do in the MD-11, then no, you can't do that.

Hope that answer your question.

You can in a way in the A310. As Alexair says, it's not quite as sophisticated as modern step climbs. All it will really do is tell you when to climb, to reach an altitude at a waypoint. You do this by RSK'ing the waypoint in your F-PLN you want to reach your new CRZ FL at, this will open VERT REV. If you're at your current CRZ FL, there should be a STEP PRED> prompt, which will allow you to tell the FMS "Hey, I want to be at this new CRZ ALT at this waypoint" and the FMS will tell you when to climb. Step climbs in the A310 are not automatic, not based on optimum time to climb; and you can only have one loaded at a time.