  Using realistic wave functions, the proton-neutron and proton-proton momentum
distributions in $^3He$ and $^4He$ are calculated as a function of the
relative, $k_{rel}$, and center of mass, $K_{CM}$, momenta, and the angle
between them. For large values of ${k}_{rel}\gtrsim 2\,\,fm^{-1}$ and small
values of ${K}_{CM} \lesssim 1.0\,\,fm^{-1}$, both distributions are angle
independent and decrease with increasing $K_{CM}$, with the $pn$ distribution
factorizing into the deuteron momentum distribution times a rapidly decreasing
function of $K_{CM}$, in agreement with the two-nucleon (2N) short range
correlation (SRC) picture. When $K_{CM}$ and $k_{rel}$ are both large, the
distributions exhibit a strong angle dependence, which is evidence of
three-nucleon (3N) SRC. The predicted center-of-mass and angular dependence of
2N and 3N SRC should be observable in two-nucleon knock-out processes
$A(e,e'pN)X$.
