  We present a theoretical investigation on the pulsational behavior of
metal-rich RR Lyrae variables over the range of evolutionary parameters
suitable for stars with metallicities Z= 0.006, 0.01 and 0.02. With the
addition of similar results for metal-poor pulsators we discuss the theoretical
pulsational scenario covering the metallicity range from Z=0.0001 to 0.02. We
find that the distribution of field ab-type RR Lyrae stars in the
period-metallicity plane can be easily understood within the framework of the
present theoretical scenario, suggesting that the Oosterhoff dichotomy also
affects field variables. Theoretical predictions concerning the
amplitude-period diagram are discussed and compared with observational data. We
find a general agreement for metal-poor ([Fe/H]<-1.4) RR Lyrae stars, whereas
more metal-rich variables show amplitudes smaller than those predicted for
pulsators originated from old, low-mass evolving stars. Alternatively, the
agreement between theory and observations would require that a substantial
fraction of metal-rich RR Lyrae variables in the Galactic field were younger
than approximately 2 Gyr. The comparison between the pulsational behavior of RR
Lyrae either in the Galactic field or in the Galactic bulge discloses the
evidence that, at least as far as RR Lyrae variables are concerned, the
metal-rich components of the bulge and of the field population appear quite
similar.
