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Many satellite and ground observations point at anomalous ionospheric phenomena associated with seismic activity. It was shown that some ionospheric effects before earthquakes can be explained by acoustic gravity waves (AGW) influence on the ionosphere. One of possible sources of these waves can be greenhouse effect gases penetrating from the lithosphere to near ground atmospheric layer. An accurate numerical model of a lithospheric gas source, excitation and propagation of AGW field to the near-source region with altitudes up to the ionospheric F region is used. The model includes effective boundary conditions on the ground level and takes into account reactive (non-propagating) AGW modes. Numerical convergence is proven. Presence of reactive modes leads to a change of AGW velocity amplitude at altitude 250 km by an order of value and in 4 times for AGW with periods 15 min. and 1 hour, respectively. Electron concentration disturbances in the ionospheric Fregfion before earthquakes can reach a value of the order of few dozens percents for AGW with period 1 hour, which agrees with the results of observations. Ionospheric response to AGW, namely, relative change of electron concentration at altitude 250 km reaches a maximum for AGW with period equal to 73 min for a given (bell-shaped) spatial dstribution of lithospheric gas source with width 100 km. Spatial distribution of electron concentration disturbances are non-symmetrical in the oblique geomagnetic field. "Twin-source" of AGW in the lithosphere can pronounce itself in a splitting of spatial distribution of relative change of electron concentration..