The measurement of cosmological parameters is investigated in a representation of the least-action method that uses a redshift-space data set to simultaneously constrain the real-space fields δ and . This method is robust in recovering the entire evolution of the matter density contrast and peculiar velocities of galaxies in real space from current galaxy redshift surveys. The main strength of the method is that it permits us to break the degeneracy of the parameters b and Ωm (customarily measured in the ratio β ≡ Ω/b from redshift-space distortions), and these are evaluated separately in the current context. The procedure provides a simple numerical means to extract as much information as possible from a given sample, in the simplest linear bias model, before resorting to cosmic complementarity to resolve the degeneracy in the measurement of Ωm. The same premise applies to more sophisticated choices of bias models. We construct a likelihood parameter λ(Ωm,b) to evaluate the relative likelihood of different values of b and Ωm. The method is applied to the IRAS 1.2 Jy redshift survey with a low-resolution Gaussian smoothing length of 1200 km s-1 within a spherical region xmax ~ 15,000 km s-1, and the reconstructed velocity field is then compared with POTENT-reconstructed velocities from the Mark III radial-velocity data set within a radius of ~5000 km s-1, which have been suitably prepared to account for Malmquist bias and other systematic errors. The analysis yields a likelihood for the parameters that is overall consistent with Ωm ≈ 0.3 and b ≈ 1.1, thus lending support to a nonvanishing cosmological constant ΩΛ ≈ 0.7 in a flat universe.