The contributions of all higher-order phaseshifts (virtually up to infinity), as given by Ali and Fraser (1977), to the total momentum-transfer and viscosity cross sections for elastic electron-atom (e-a) collisions are evaluated analytically. The magnitude and significance of these contributions are discussed in terms of the dependence on the truncation value of the electron angular momentum l* at low and intermediate electron energies, and on the polarization characteristics of the rare-gas atom. The importance of the quadrupole polarization potential in determining the respective truncation errors is pointed out.