We report ultrasonic dispersion and attenuation measurements near the liquid-gas critical point of 3He at frequencies from 0.5 to 5.0 MHz and densities from O. 89pc to i. 15pc. The singular part of the sound attenuation and the dispersion on the critical isochore pc = O. 0414 g/ cm 3 are analyzed in terms of the Kawasaki-Mistara theory. If the Ornstein-Zernike order parameter correlation function is assumed in the analysis, good agreement with our data is achieved, except close to the critical temperature Tc in the high-frequency region, where to* = to/toD >> 1. Here toD is the characteristic relaxation rate of the critical fluctaations. From a fit of the theory to our data, and assuming the inverse correlation length K is expressed by K = roe ~, where e = (T-Tc)/Tc with ~ = 0.63, we obtain Ko = (3.9โข 109 m -1. It is found that a more realistic form of the correlation function, as proposed by Fisher and Langer and calculated by Bray, yields even poorer agreement with out data than does the classical Ornstein-Zernike form for to * > i0. The same difficulties appear in the analysis of the available data for xenon. Thus, the present mode coupling theory is unable to satisfactorily describe the acoustic experiments on fluids near the liquid-vapor critical point over a large range of reduced frequencies to*. In the appendix, we reanalyze previously reported ultrasonic data in 4He, taking into account the nonsingular term of the thermal conductivity. Using u = 0.63, we obtain a good fit of the experiment to the theory in the hydrodynamic region with Ko = (5.5+ I) x 109 m -1.