A theory is presented to describe the dynamics of multiline parametric SRS (PSRS) in a highly transient regime. The PSRS conversion of the biharmonical pump at laser and Ist Stokes frequencies may generate Raman components filling the bandwidth up to Delta nu/nu = 1.4 (two octaves on level of 0.1 to peak) with a bandwidth buildup time much less than time T-2 of the Raman medium at modest experimental conditions.