  Homogenization of a scalar elliptic equation in a bounded domain with Neuman
boundary condition is studied. Coefficients of the operator are oscillating
over two different groups of variables with different small periods
$\varepsilon$ and $\delta=\delta(\varepsilon)$. We assume that
${\delta}/{\varepsilon}$ tends to zero as $\varepsilon$ tends to zero. It is
known that the limit problem is obtained through reiterated homogenization
procedure and corresponds to an elliptic equation with constant coefficients.
The difference for resolvents of the initial and the limit problems is
estimated in operator $(L^2\to L^2)$-norm. This estimate is of order
$\tau=\tau(\varepsilon)$ which is the maximum of $\ve$ and
${\delta}/{\varepsilon}$. We find also the approximation of the initial
resolvent in operator $(L^2\to H^1)$-norm, it is of order $\sqrt{\tau}$.
