  (Abridged). We present HST photometry of the late-type dwarf galaxy NGC 1705
observed with the WFPC2 in the U and B bands, and with the ACS/HRC in the U, V,
and I bands. We cross-correlate these data with previous ones acquired with the
WFPC2 in V and I and derive multiband Color-Magnitude diagrams (CMDs) of the
cross-identified individual stars and candidate star clusters. For the central
regions of the galaxy, where HST-NICMOS J and H photometry is also available,
we present U, B, V, I, J, H CMDs of the 256 objects with magnitudes measured in
all bands. While our previous study based on V, I, J and H data allowed us to
trace the star formation history of NGC 1705 back to a Hubble time, the new
data provide a better insight on its recent evolution. With the method of the
synthetic CMDs, we confirm the presence of two strong bursts of star formation
(SF). The older of the two bursts (B1) occurred between ~ 10 and 15 Myr ago,
while the younger burst (B2) started ~ 3 Myr ago, and it is still active. The
stellar mass produced by B2 amounts to ~ 10^6 msun, and it is a factor of ~ 3
lower for B1. The interburst phase was likely characterized by a much lower
level of SF rather than by its complete cessation. The two bursts show distinct
spatial distributions: while B1 is centrally concentrated, B2 is more diffused,
and presents ring and arc-like structures that remind of an expanding shell.
This suggests a feedback mechanism, in which the expanding superbubble observed
in NGC 1705, likely generated by the (10-15) Myr burst, triggered the current
strong SF activity. From the HRC data, we identified 12 star clusters (plus the
SSC) in the central region of NGC 1705, 10 of which have photometry in all the
UBVIJH bands. Using the GALEV models, we derived ages from ~ 10 Myr to ~ 1 Gyr,
and masses between ~ 10^4 and 10^5 msun for the clusters.
