Optimal polarized observables for model-independent new physics searches at the linear collider

We discuss the sensitivity to four-fermion contact interactions of the process of fermion-pair production at the e^+ - e^- Linear Collider (LC), with E_{CM}=0.5 TeV and longitudinally polarized electron beam. The analysis is based on polarized integrated cross sections with optimal cuts. Beam polarization and optimization are shown to have a crucial role in the derivation of model-independent constraints on the new interactions from the data.