The excitation and emission spectra of alkali-metal atoms (Cs and Rb) in liquid helium are studied. The helium pressure is changed from the saturated vapor pressure to about 29 atm at 1.6 K, under which conditions the liquid helium is in a superfluid state: The pressure shift and broadening of the observed spectra corresponding to the D lines are explained qualitatively by a theoretical calculation based on the spherical atomic bubble model. The Cs D-2 excitation spectra are found to have double peaks, indicating the existence of anisotropic oscillations of the bubble surface. The disappearance of the D-2 emission lines and the pressure-dependent quenching of the Rb D-1 emission lines are also discussed.