The least-action principle (LAP) method is used on four galaxy redshift surveys to measure the density parameter Omega_m and the matter and galaxy-galaxy power spectra. The datasets are PSCz, ORS, Mark III and SFI. The LAP method is applied on the surveys simultaneously, resulting in an overconstrained dynamical system that describes the cosmic overdensities and velocity flows. The system is solved by relaxing the constraint that each survey imposes upon the cosmic fields. A least-squares optimization of the errors that arise in the process yields the cosmic fields and the value of Omega_m that is the best fit to the ensemble of datasets. The analysis has been carried out with a high-resolution Gaussian smoothing of 500 km/s and over a spherical selected volume of radius 9,000 km/s. We have assigned a weight to each survey, depending on their density of sampling, and this parameter determines their relative influence in limiting the domain of the overall solution. The influence of each survey on the final value of Omega_m, the cosmographical features of the cosmic fields and the power spectra largely depends on the distribution function of the errors in the relaxation of the constraints. We find that PSCz and Mark III are closer to the final solution than ORS and SFI. The likelihood analysis yields Omega_m= 0.37\pm 0.01 to 1sigma level. PSCz and SFI are the closest to this value, whereas ORS and Mark III predict a somewhat lower Omega_m. The model of bias employed is a scale-dependent one, and we retain up to 42 bias coefficients b_{rl} in the spherical harmonics formalism. The predicted power spectra are estimated in the range of wavenumbers 0.02-0.49h Mpc^{-1}, and we compare these results with measurements recently reported in the literature.

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