While the optical breakdown of transparent dielectrics for nanosecond and longer laser pulses is well investigated theoretically and experimentally, the breakdown in a field of picosecond and femtosecond pulses has not been adequately explored. At the same time such investigation presents scientific interest, because short pulse duration can make some change for a mechanism of the optical breakdown. Also these data have practical importance for high energy laser development and management of temporal parameters of a pulse. Thus we have carried out measurements of the damage thresholds for pulse durations 450 ps and 3 ps (FWHM) for fused silica. Theoretical analysis is presented to explain experimental results. The possibility of applying the optical breakdown for pulse shortening is discussed.