A finite-width laser pulse of high intensity propagating in an underdense plasma excites a transversely inhomogeneous, finite amplitude wakefield. This wake wave undergoes a transverse wave breaking due to the increase of the wake front curvature, followed by the self-intersection of electron trajectories. Transverse break occurs at much lower wave amplitudes than the conventional one-dimensional wave break. The resulting structures have generic forms that can be described by modified curves parallel to a parabola. Simulations with the particle-in-cell electromagnetic relativistic code VLPL2D show such structures appearing. {copyright} {ital 1997} {ital The American Physical Society}