  The approximation of the renormalized stress-energy tensor of the quantized
massive scalar field in Reissner-Nordstr\"om spacetime is constructed. It is
achieved by functional differentiation of the first two nonvanishing terms of
the Schwinger-DeWitt expansion involving the coincidence limit of the
Hadamard-Minakshisundaram-DeWitt-Seely coefficients $[a_{3}]$ and $[a_{4}]$
with respect to the metric tensor. It is shown, by comparison with the existing
numerical results, that inclusion of the second-order term leads to substantial
improvement of the approximation of the exact stress-energy tensor. The
approximation to the field fluctuation, $\langle \phi^{2} \rangle,$ is
constructed and briefly discussed.
