We perform modal analysis and ultracold atomic beam propagation in hollow optical fibers. The eigenmodes and modal propagation constants of the atomic waveguide are determined by numerical solution of the Schrodinger equation for the center-of-mass motion. The existence of a threshold de Broglie wavelength for the fundamental mode is predicted. Beam propagation is performed by modal expansion of the wavefunction on a truncated basis of eigenmodes of the atomic waveguide. The evolution of the atomic probability density profile along the waveguide for a non cylindrical atomic beam is shown.