  We study the phase diagram of R_{1-x}A_xMnO_3 (R=La, Pr, Nd, Sm ; A=Ca, Sr,
Ba) by taking into account the degeneracy of $e_g$ orbitals and the anisotropy
of the transfer integral. The electron-electron interaction is treated in the
mean field approximation with the optimization of the spin and orbital
structures. The global phase diagram is understood in terms of the two
interactions, i.e., the super exchange interaction for small $x$ and the double
exchange interaction for larger $x$ modified by the orbital degeneracy. The
dimensionality of the electronic energy band resulting from the orbital
structure is essential to determine the phase diagram. The effects of the
Jahn-Teller distortion are also studied.
