  Let D be a smooth bounded pseudoconvex domain in C^n. We give several
characterizations for the closure of D to have a strong Stein neighborhood
basis in the sense that D has a defining function r such that {z\in C^n:r(z)<a}
is pseudoconvex for sufficiently small a>0. We also show that this condition is
invariant under proper holomorphic maps that extend smoothly to the boundary.
