We present a physics-based non-equilibrium plasma model for Laser Induced Breakdown (LIB). Here, we consider the influence of mode-beating pulse on the plasma generation. The system of chemically reactive Navier-Stokes equations describes the hydrodynamics and non-equilibrium effects are accounted for by means of a two-temperature model for heavy-particles and free-electrons. The non-equilibrium radiation model is based on a kinetic approach for the photons (radiative transfer equation formulation). Inverse Bremsstrahlung, multiphoton ionization, chemical kinetics and shock wave dynamics are taken into account. Simulations were conducted in quiescent ambient air at atmospheric pressure. The computed absorbed energy is in good agreement with the experiments for both the single-mode and multi-mode laser operating configuration; the kernel formation and dynamics depends on the mode-beating pulse shape, as observed experimentally. The kernel structure for the multi-mode configuration appears periodic, with the distance between the scattered spots being a function of the modulating frequency.