A complete sample of 659 field galaxies with 17.0 < U \leq 21.1 , each with U-B-V-R-I7500-I8600 photometry , has been selected from a deep field survey which covers 0.83 deg ^ { 2 } along six lines of sight ( Hall et al .
1996a ) .
Each galaxy ’ s spectral type and redshift has been estimated using a multicolor photometric technique ( Liu & Green 1998 ) .
Total number counts of the galaxies in the U-band give a count slope d ( logN ) /dM = 0.55 \pm 0.05 , consistent with previous studies .

The 545 galaxies in the sample classified as spectral type Sbc or bluer are analyzed for signs of evolution with redshift , and for unusual star formation histories .
The U-band luminosity function of these blue galaxies at 0.02 < z < 0.15 has a steep \alpha \simeq -1.85 down to M ( B ) \simeq -14 .
The luminosity functions at 0.15 \leq z < 0.3 and 0.3 \leq z \leq 0.5 show significant evolution in M* and \phi* , at levels consistent with those found in the Canada-France and Autofib Redshift Surveys .

A significant population of very blue ( rest frame U-B < - 0.35 ) galaxies , with spectral energy distributions indicating strong starburst activity , is observed at z \gtrsim 0.3 but not at z < 0.3 .
This population is confirmed via spectroscopy of part of the sample .
These may be galaxies temporarily brightened by global starbursts , which subsequently fade and redden at lower redshifts .