  The decays of $B$ mesons to a pair of charmless pseudoscalar ($P$) mesons are
analyzed within a framework of flavor SU(3). Symmetry breaking is taken into
account in tree ($T$) amplitudes through ratios of decay constants; exact SU(3)
is assumed elsewhere. Acceptable fits to $B \to \pi \pi$ and $B \to K \pi$
branching ratios and CP asymmetries are obtained with tree, color-suppressed
($C$), penguin ($P$), and electroweak penguin ($P_{EW}$) amplitudes. Crucial
additional terms for describing processes involving $\eta$ and $\eta'$ include
a large flavor-singlet penguin amplitude ($S$) as proposed earlier and a
penguin amplitude $P_{tu}$ associated with intermediate $t$ and $u$ quarks. For
the $B^+ \to \pi^+ \eta'$ mode a term $S_{tu}$ associated with intermediate $t$
and $u$ quarks also may be needed. Values of the weak phase $\gamma$ are
obtained consistent with an earlier analysis of $B \to VP$ decays, where $V$
denotes a vector meson, and with other analyses of CKM parameters.
