We present a development of the dipole moment and polarizability operators Of X2Y4 molecules, using a tensorial formalism analogous to the one developed for tetrahedral and octahedral molecules [V. Boudon, J.-P. Champion, T. Gabard, M. Loete, F. Michelot, G. Pierre, M. Rotger, Ch. Wenger, M. Rey, J. Mol. Spectrosc. 228 (2004) 620-634]. These operators are involved in the calculation of the intensities of rovibrational transitions as well as in the calculation of the Stark effect. Expressions for the matrix elements are derived. A model for the study of the Stark effect in isolated bands of such molecules is proposed and has been used to predict the Stark spectra of the v(12) band of ethylene. Values of the polarizability coefficients have been calculated using ab initio methods.