We present J and Ks band galaxy counts down to J=24 and Ks=22.5 obtained wi
th the new infrared imager/spectrometer, SOFI, at the ESO New Technology Te
lescope. The co-addition of short, dithered, images led to a total exposure
time of 256 and 624 minutes respectively, over an area of similar to 20 ar
cmin(2) centered on the NTT Deep Field. The total number of sources with S/
N> 5 is 1569 in the J sample and 1025 in the Ks-selected sample. These are
the largest samples currently available at these depths. A dlogN/dm relatio
n with slope of similar to 0.36 in J and similar to 0.38 in Ks is found wit
h no evident sign of a decline at the magnitude limit. The observed surface
density of "small" sources is much lower than "large" ones at bright magni
tudes and rises more steeply than the large sources to fainter magnitudes.
Fainter than J similar to 22.5 and Ks similar to 21.5, small sources domina
te the number counts. Galaxies get redder in J-K down to J similar to 20 an
d Ks similar to 19. At fainter magnitudes, the median color becomes bluer w
ith an accompanying increase in the compactness of the galaxies. We show th
at the blue, small sources which dominate the faint IR counts are not compa
tible with a high redshift (z > 1) population. On the contrary, the observe
d color and compactness trends, together with the absence of a turnover at
faint magnitudes and the dominance of small sources, can be naturally expla
ined by an increasing contribution of sub-L* galaxies when going to fainter
apparent magnitudes. Such evidence strongly supports the existence of a st
eeply rising (alpha << - 1) faint end of the local infrared luminosity func
tion of galaxies - at least for luminosities L < 0.01L*.