  A generalized Kadomtsev-Petviashvili equation (GKPE) $(u_t+u u_x + \beta(t)u
+\gamma(t)u_{xxx})_x+\sigma(t)u_{yy}\ = \ 0$ is shown to admit an
infinite-dimensional Lie group of symmetries when $\bt(t), \ga(t)$ and $\si(t)$
are arbitrary. The Lie algebra of this symmetry group contains two arbitrary
functions $f(t)$ and $g(t)$. Further, low-dimensional subalgebras and
physically meaningful five dimensional Lie algebra containing translation and
Galilei transformation are derived. A solution of GKPE involving two arbitrary
functions of time $t$, in addition to $f(t)$ and $g(t)$, is obtained using an
one-dimensional subalgebra.
