  The aim of this paper is to study the evolution of the broadband spectrum of
one of the brightest and nearest quasars 3C 273.
  We analyze the data obtained during quasi-simultaneous INTEGRAL and XMM
monitoring of the blazar 3C 273 in 2003--2005 in the UV, X-ray and soft
gamma-ray bands and study the results in the context of the long-term evolution
of the source.
  The 0.2-100 keV spectrum of the source is well fitted by a combination of a
soft cut-off power law and a hard power law. No improvement of the fit is
achieved if one replaces the soft cut-off power law by either a blackbody, or a
disk reflection model. During the observation period the source has reached the
historically softest state in the hard X-ray domain with a photon index
$\Gamma=1.82\pm 0.01$. Comparing our data with available archived X-ray data
from previous years, we find a secular evolution of the source toward softer
X-ray emission (the photon index has increased by $\Delta\Gamma\simeq 0.3-0.4$
over the last thirty years). We argue that existing theoretical models have to
be significantly modified to account for the observed spectral evolution of the
source.
