K~y WORDS: quartic potential oscillator, Schr~dinger operator, semiclassical asymptotics of eigenvalues, quasimodes, Gelfand-Lidskii index.For the two parameter Schrfdinger operator with parameters (e, h) and with the family of potentials V'(z)=z~x~2 q-~(zle 4q_m2) ,, m=(mI,x2) ER 2, e_>0,we consider the problem of constructing the semiclassical (/i ~ 0) asymptotics of eigenvalues and eigenhmctions,uniformly with respect to the regular parameter e in a domain ft C R~ + . The quartic potential model (1) is presently one of the most popular models in the problem of semiclassical quantization of nonintegrable Hamiltonian systems with chaotic behavior (e.g., see [1,2]). The nonintegrability of the classical system (corresponding to (1))with the IIamiltonian H~(x, p) --pa/2 + Ve(z) is confirmed by numerical experiments [3][4][5]. In [6] it was proved that there does not exist an additional analytic integral of motion for ~ ~ 1, 1/3. It is well known that the semiclassical approximation to multidimensional spectral problems of quantum mechanics allows one to assign subsequences of asymptotic eigenvalues and asymptotic eigenfunctions (quasimodes of the corresponding Humiltonian) to some invariant objects of the classical system [1, 2]. For nonintegrable systems that possess a family of invariant k-dimensional isotropic tori A t (0 _< k < n, where n is the dimension of the problem), formulas for quasimodes are obtained by the complex WKB method (Maslov's complex germ theory) [7][8][9] under additional stability type conditions (in the linear approximation) for these objects. In the simplest case k = 0 (for stationary points of the Humiltonian system), the semiclassical approximation coincides with the oscillator approximation, which is well known in physics. In the most studied case k = 1 (see [7,[10][11][12][13][14]), the orbital stability of dosed phase trajectories A 1 is a sttfllcient condition for quasimodes to exist and to be constructed (rood O(/ia/2)); a quantization condition of Bohr-Sommerfeld type must also be satisfied (see [8,9]).The nonintegrable system (3) has families of closed trajectories related in a natural way to the group C4~ of discrete symmetries of the potential V~(z). Let us consider the following improper rotations of the plane: reflections Oi: xi ~ -zi, i = 1,2, with respect to the coordinate axes and 04-: xl ~-~ :kzu with respect to the diagonals. Let us also consider the corresponding linear canonical transformations of the phase space, which commute with the Hamiltonian H~(x, p): Gi : xl ~ -xi, Pi ~-* -pi, i = 1,2, and G• ~-* +x2,pl ~ +P2. The fixed points II~ = (xi =pl = 0) and II4-= (xl = +z2, pl = q'p2) of these mappings form two-dimensional symplectic planes. Obviously, these points are invaxiant with