This is the first paper in a series aimed at defining a statistically
significant sample of QSOs in the range 15<B<18.75 and 0.3<z<2.2.
The selection is carried out using direct plates obtained at the ESO and UK
Schmidt Telescopes, scanned with the COSMOS facility and searched for objects
with an ultraviolet excess. Follow-up spectroscopy, carried out at ESO La
Silla, is used to classify each candidate. In this initial paper, we describe
the scientific objectives of the survey; the selection and observing techniques
used. We present the first sample of 285 QSOs (MB​<−23) in a 153 deg2
area, covered by the six ``deep'' fields, intended to obtain significant
statistics down B≃18.75 with unprecedented photometric accuracy. From
this database, QSO counts are determined in the magnitude range 17<B<18.75.Comment: 21 pages uuencoded compressed postscript, to appear in Astronomy and
Astrophysics Supplements, 199