The deconfining ponderomotive force exerted by an intense electromagnetic wave on a linearly inhomogeneous plasma layer has been analytically investigated. Since the ponderomotive force maximizes near the region where the dielectric constant&egr;′ → 0, an exact solution of the wave equation is required for a correct estimate of the maximum force. For the case of oblique incidence with the electric vector in the plane of incidence, the solution of the exact wave equation leads to an interesting resonance effect which predicts a force higher than that obtained by earlier workers using a WKB procedure. Physically, this enhanced ponderomotive force arises because of the large nonuniform longitudinal fields that are generated in the region&egr;′ ≈ 0for this geometry.