  We argue that the tri-bimaximal neutrino mixing pattern $V_0$ or its
generalized form $V'_0$, which includes two arbitrary Majorana phases of CP
violation, may result from an underlying flavor symmetry at a superhigh energy
scale close to the seesaw scale ($\sim 10^{14}$ GeV). Taking the working
assumption that three neutrino masses are nearly degenerate, we calculate
radiative corrections to $V_0$ and $V'_0$ in their evolution down to the
electroweak scale ($\sim 10^2$ GeV). Three mixing angles of $V_0$ or $V'_0$ are
essentially stable against radiative corrections in the standard model (SM). In
the minimal supersymmetric standard model (MSSM), however, $V_0$ is in general
disfavored and $V'_0$ can be compatible with current neutrino oscillation data
if its two Majorana phases $\alpha^{}_1$ and $\alpha^{}_2$ are properly
fine-tuned. We also find that it is possible to radiatively generate the
CP-violating phase $\delta$ from $\alpha^{}_1$ and $\alpha^{}_2$, and \delta
may keep on staying at its fixed point in either the SM or the MSSM.
