  A combination of Hubble Space Telescope (HST) WFPC2 and NICMOS images are
used to investigate the gas/dust and stellar structure inside the central 300
pc of the nearby active galaxy NGC 4303.
  The NICMOS H-band (F160W) image reveals a bright core and a nuclear elongated
bar-like structure of 250 pc in diameter. The bar is centered on the bright
core, and its major axis is oriented in proyection along the spin axis of the
nuclear gaseous rotating disk recently detected (Colina & Arribas 1999).
  The V-H (F606W - F160W) image reveals a complex gas/dust distribution with a
two-arm spiral structure of about 225 pc in radius. The southwestern arm is
traced by young star-forming knots while the northeastern arm is detected by
the presence of dust lanes. These spirals do not have a smooth structure but
rather they are made of smaller flocculent spirals or filament-like structures.
The magnitudes and colors of the star-forming knots are typical of clusters of
young stars with masses of 0.5 to 1 x $10^5 M_{solar}, and ages of 5 to 25
million years.
  The overall structure of the nuclear spirals as well as the size, number and
masses of the star-forming knots are explained in the context of a massive
gaseous nuclear disk subject to self-gravitational instabilities and to the
gravitational field created by the nuclear bar. According to the model, the
gaseous disk has a mass of about 5 x 10^7 M_{solar} inside a radius of 400 pc,
the bar has a radius of 150 pc and a pattern speed of about 0.5 Myr^{-1}, and
the average mass accretion rate into the core (R < 8 pc) is about 0.01
M_{solar}$ yr^{-1} for about 80 Myr.
