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Observations of interstellar extinction and polarization indicate that theinterstellar medium consists of aligned non-spherical dust grains which showvariation in the interstellar extinction curve for wavelengths ranging from NIRto UV. To model the extinction and polarization, one cannot use the Mie theorywhich assumes the grains as solid spheres. We have used a T-matrix based methodfor computing the extinction efficiencies of spheroidal silicate and graphitegrains of different shapes (axial ratios) and sizes and used these efficienciesto evaluate the interstellar extinction curve in the wavelength range 3.4--1.0microns. A best fit linear combination of silicate and graphite grains of notvery large axial ratio, fits the observed extinction curve reasonably well.  We calculate the volume extinction factor Vc, which is an important parameterfrom the point of view of the cosmic abundance, for the spheroidal grain modelsthat reproduce the interstellar extinction curve. We find that the shape of thegrains do not affect the volume extinction factor.  Finally we have also studied the extinction and linear polarizationefficiencies for aligned spheroids. The results show that the shape of grainsaffects the linear polarization efficiencies considerably for variousorientation angles of the spheroids.Comment: 10 pages, 6 figure To appear in A & A, 200

Interstellar extinction by spheroidal dust grains