A narrow bundle of monochromatic acoustic waves is reflected from an irregular sea surface. The elevations of the surface are normally distributed with a relatively narrow power spectrum. The characteristic width of the active scattering area is small as compared to the correlation distance of the irregular waves. A stochastic model is devised for the surface waves in which the amplitude and frequency of these waves vary linearly over the active scattering area. Starting from the Helmholtz equation and using the Kirchhoff approximation, first‐order expressions are derived for the average amplitude and phase variation of the reflected waves. The expression for the average amplitude of the reflected waves depends on the width of the incoming sound bundle. However, for short waves this expression becomes independent of the width and reduces to the familiar result of Eckart when the angle of incidence is equal to the angle of observation. The phase variation is independent of the width of the scattering area and has its largest values when the inverse acoustic wave number has the same order of magnitude as the root‐mean‐square value of the surface‐wave height.