lightest neutrino $m_1$ [@PPW; @WR0302; @PPSNO2bb]. Information on absolute values of neutrino masses in the range of interest can also be obtained in the [$\mbox{}^3 {\rm H}$ $\beta$-decay ]{}neutrino mass experiment KATRIN [@KATRIN] and from cosmological and astrophysical data (see, e.g., refs. [@Weiler2001; @Hu99]).

Rather stringent upper bounds on have been obtained in the $^{76}$Ge experiments by the Heidelberg-Moscow collaboration [@76Ge00], $ {\mbox{$\left|  < \! m  \! > \right| \ $}}\!\! < 0.35~{\rm eV}$ ($90\%$ C.L.), and by the IGEX collaboration [@IGEX00], ${\mbox{$\left|  < \! m  \! > \right| \ $}}\!\! < (0.33 \div 1.35)~{\rm eV}$ ($90\%$ C.L.). Taking into account a factor of 3 uncertainty in the calculated value of the corresponding nuclear matrix element, we get for the upper limit found in [@76Ge00]: ${\mbox{$\left|  < \! m  \! > \right| \ $}}\!\! < 1.05$ eV. Considerably higher sensitivity to the value of ${\mbox{$\left|  < \! m  \! > \right| \ $}}$ is planned to be reached in several ${\mbox{$(\beta \beta)_{0 \nu}  $}}$-decay experiments of a new generation. The NEMO3 experiment [@NEMO3], which began to take data in July of 2002, and the cryogenics detector CUORICINO [@CUORE] to be operative in the second half of 2002, are expected to 