  As a result of the reanalysis of the OGLE-I observations by means of the
image subtraction method, we present the first part of a catalog, consisting of
the data for variable stars in four Galactic fields observed by the OGLE-I,
viz. MM1-A, MM1-B, MM7-A, and MM7-B. In total, 2016 variable stars have been
found. This increased the number of known variable in these fields stars more
than twofold. We comment on the detectability of the variable stars in previous
studies.
  Some interesting findings are also discussed. Among others, we found 45 Delta
Scuti stars (38 are new) including several multiperiodic objects. Detailed
analysis of the light curves of 47 RR Lyrae stars (24 are new detections)
allowed us to find five stars which exhibit nonradial pulsations and one RRd
star. Three RRab stars are members of the Sagittarius dwarf galaxy (Sgr dSph).
We also find four objects which are probably galactic RV Tauri stars and one W
Virginis star which seems to belong to Sgr dSph. This is the first Population
II Cepheid found in this satellite galaxy and dSph other than the Fornax one.
  For eclipsing EW-type binaries, which are the most abundant variables in our
catalog, we investigate the amplitude and period distributions. A comparison
with the previous OGLE-I catalogs indicates that we found more stars with
smaller amplitudes. Finally, in addition to the two microlensing events
discovered previously in these fields, we find five more.
