We demonstrate that short laser pulse self-guiding
over distances of many Rayleigh lengths can be achieved
in the absence of any focusing nonlinearity as a result
of trapping of a leaking wave in a plasma channel produced
by field-induced ionization in the saturation regime. A
detailed computational study of the new self-guiding effect
in both cases of comparatively long laser pulses, when
the traditional approximation of the slowly varying complex
amplitude is valid, and of high intense ultrashort laser
pulses comprising only few field cycles have been performed.