Results are presented on the X-ray properties of 9 high-redshift (1.2
< z < 3.4) radio-loud quasars (RLQs) observed by the Advanced Satellit
e for Cosmology and Astrophysics (ASCA; 10 observations) and ROSAT (11
observations, for a subset of six quasars). New ASCA observations of
S5 0014+81 (z = 3.38) and S5 0836+71 (z = 2.17) and ROSAT observations
of PKS 2126-158 for which results were never presented elsewhere are
included. A simple model consisting of a power law plus cold, uniform
absorption gives acceptable fits to the spectra of all sources. The AS
CA spectra of the six brightest objects show evidence for absorption i
n excess of the Galactic value at a much greater than 99% confidence l
evel. Comparison with the ROSAT data suggests that absorption has sign
ificantly varied (Delta N-H similar to 8 x 10(20) cm(-2)) in the case
of S5 0836+71, on a time-scale of approximately 0.8 yr in the quasar f
rame. For the remaining five sources for which ROSAT spectra were avai
lable, the two instruments gave consistent results, and the data were
combined yielding unprecedented spectral coverage (typically about 0.4
-40 keV in the quasar frame) for high-z quasars. This allows us to put
severe limits on several different descriptions of the continuum (e.g
., broken power law, bremsstrahlung, reflection component). No Fe K al
pha emission line is detected in any of the ASCA spectra. An absorptio
n edge consistent with Fe K alpha at the quasar redshift is marginally
detected in S5 0014+81. Possible origins for the observed low energy
absorption are discussed. In particular, contributions from the molecu
lar clouds and dust present in our Galaxy (usually disregarded) are ca
refully considered. In light of the new results for S5 0836+71 and S5
0014+81, absorption intrinsic to the quasars is considered and discuss
ed. The average slope obtained from the eight ASCA spectra in the obse
rved similar to 0.5-10 keV energy band is [Gamma(0.5-10) keV] similar
or equal to 1.61 +/- 0.04, with a dispersion sigma(0.5-10 keV) similar
or equal to 0.10 +/- 0.03, The average photon index in the observed 2
-10 keV band, where the effect of absorption is negligible, is [Gamma(
2-10 keV)] similar or equal to 1.53 +/- 0.05, with a dispersion sigma(
2-10 keV) less than or similar to 0.12. Furthermore, the implications
of the present results on the calculations of the contribution of quas
ars to the cosmic X-ray and gamma-ray backgrounds are briefly discusse
d.