The linear evolution of the Rayleigh-Taylor instability (RTI) at the ablation front of a laser irradiated toil is studied by high resolution two dimensional Lagrangian hydrodynamic simulations, with simple initialization of the perturbation. Laser and target parameters relevant to reactor-size direct-drive laser fusion targets are considered. Growth rates smaller than the classical value and full stabilization at short wavelength are found. The results are well fitted by a dispersion relation of the form suggested by Takabe et al., with the parameters alpha = 0.9 and beta = 2.3, which can also reproduce the time dependent evolution of the growth rate, for weakly varying flow parameters.