  We present the results of an extensive campaign of coordinated X-ray (ROSAT)
and UV (IUE) observations of the symbiotic star AG Dra during a long period of
quiescence (1990-1993) followed by two optical outbursts in 1994 and 1995. The
hot component (i.e. X-ray emitting compact object) turns out to be very
luminous during the quiescent phase: (9.5+/-1.5)*10^36 (D/2.5 kpc)^2 erg/s.
This suggests that the compact object is burning hydrogen-rich matter on its
surface even in the quiescent (as defined optically) state at a rate of
(3.2+/-0.5)*10^-8 (D/2.5 kpc)^2 M_sun/yr. Assuming a steady state, i.e. burning
at precisely the accretion supply rate, this high rate suggests a Roche lobe
filling cool companion though Bondi-Hoyle accretion from the companion wind
cannot be excluded. We have discovered a remarkable decrease of the X-ray flux
during both optical maxima. In the UV these events were characterized by a
large increase of the emission line and continuum fluxes. The anticorrelation
of X-ray/UV flux and optical brightness evolution is very likely due to a
temperature decrease of the hot component which could be the result of an
increased mass transfer to the burning compact object, causing it to slowly
expand to about twice its original size during each optical outburst.
