We construct a relativistic potential quark model of D, Ds, B, and Bs mesons in which the light quark motion is described by the Dirac equation with a scalar-vector interaction and the heavy quark is considered a local source of the gluon field. The effective interquark interaction is described by a combination of the perturbative one-gluon exchange potential V Coul (r) = −ξ/r and the long-range Lorentz-scalar and Lorentz-vector linear potentials S l.r. (r) = (1 − λ)(σr + V0) and V l.r. (r) = λ(σr + V0), where 0 λ < 1/2. Within the quasiclassical approximation, we obtain simple asymptotic formulas for the energy and mass spectra and for the mean radii of D, Ds, B, and Bs mesons, which ensure a high accuracy of calculations even for states with the radial quantum number nr ∼ 1. We show that the fine structure of P-wave states in heavy-light mesons is primarily sensitive to the choice of two parameters: the strong-coupling constant αs and the coefficient λ of mixing of the long-range scalar and vector potentials S l.r. (r) and V l.r. (r). The quasiclassical formulas for asymptotic coefficients of wave function at zero and infinity are obtained.