  For $\a,\b>0$ and for a locally integrable function (or, more generally, a
distribution) $\f$ on $(0,\be)$, we study integral ooperators ${\frak
G}^{\a,\b}_\f$ on $L^2(\R_+)$ defined by $\big({\frak G}^{\a,\b}_\f
f\big)(x)=\int_{\R_+}\f\big(x^\a+y^\b\big)f(y)dy$. We describe the bounded and
compact operators ${\frak G}^{\a,\b}_\f$ and operators ${\frak G}^{\a,\b}_\f$
of Schatten--von Neumann class $\bS_p$. We also study continuity properties of
the averaging projection $\Q_{\a,\b}$ onto the operators of the form ${\frak
G}^{\a,\b}_\f$. In particular, we show that if $\a\le\b$ and $\b>1$, then
${\frak G}^{\a,\b}_\f$ is bounded on $\bS_p$ if and only if
$2\b(\b+1)^{-1}<p<2\b(\b-1)^{-1}$.
