  We derive analytical expressions for the excitation energy of the isoscalar
giant monopole and quadrupole resonances in finite nuclei, by using the scaling
method and the extended Thomas-Fermi approach to relativistic mean field
theory. We study the ability of several non-linear sigma-omega parameter sets
of common use in reproducing the experimental data. For monopole oscillations
the calculations agree better with experiment when the nuclear matter
incompressibility of the relativistic interaction lies in the range 220-260
MeV. The breathing-mode energies of the scaling method compare satisfactorily
with those obtained in relativistic RPA and time-dependent mean field
calculations. For quadrupole oscillations all the analyzed non-linear parameter
sets reproduce the empirical trends reasonably well.
