An explanation of discrepancies between predictions of the Kroll-Watso
n theory and cross sections measured in the Wallbank-Holmes experiment
s on electron-atom scattering in the presence of a powerful low-freque
ncy laser field is presented. Our model calculations for helium and ar
gon as target atoms come out to be in good agreement with experimental
results; i.e., obtained cross sections are by many orders of magnitud
e larger than those predicted by the Kroll-Watson theory. A mechanism
responsible for such a substantial increase of the calculated cross se
ctions is found to be due to the diffraction scattering of electrons b
y atomic obstacles. [S1050-2947(97)50912-7].