(Previous answer deleted due to revised response from OP. Pre-tax contributions are not treated as "basis".)
If your contributions are in W-2 Box 14, they have already been deducted from W-2 Box 1 (and possibly state boxes); you do not get to deduct them again. (Edit: W-2 Box 5, and possibly Box 3, will be bigger than Box 1 by the amount of these and any other pre-tax retirement contributions.) These are so-called 414(h)(2) pre-tax contributions, which are unique to state and local government pension plans (including most schools).
