  We compute in QCD perturbation theory the transverse energy carried by
gluons, quarks and antiquarks with $p_T\ge p_0\approx 2$ GeV in Pb+Pb
collisions at $\sqrt{s}=5500$ $A$GeV by using structure functions compatible
with the small-$x$ increase observed at HERA. This gives a perturbative
estimate for the energy and entropy density of the bulk system at times
$\tau\sim 0.1$ fm. The predicted initial gluon entropy density gives a lower
limit of about 2200...3400 for the final charged multiplicity. Sources of
further entropy increase are discussed.
