  We report on 4 BeppoSAX Target Of Opportunity observations of MXB 1730-335,
the Rapid Burster (RB), made during the 1998 February-March outburst. In the
first observation, approximately 20 days after the outburst peak, the X-ray
light curve showed Type II bursts at a rate of 43 per hour. Nine days later,
during the second BeppoSAX pointing, only 5 Type II bursts were detected at the
beginning of the observation. During the third pointing no X-ray bursts were
detected and in the fourth and final observation the RB was not detected at
all. Persistent emission from the RB was detected up to 10 keV during the first
three pointings. The spectra of the persistent and bursting emissions below 10
keV were best fit with a model consisting of two blackbodies. An additional
component (a power law) was needed to describe the 1-100 keV bursting spectrum
when the persistent emission was subtracted. To our knowledge, this is the
first detection of the RB beyond 20 keV. We discuss the evolution of the
spectral parameters for the bursting and persistent emission during the
outburst decay. The light curve, after the second BeppoSAX pointing, showed a
steepening of the previous decay trend, and a sharper decay rate leading to
quiescence was observed with BeppoSAX in the two subsequent observations. We
interpret this behaviour as caused by the onset of the propeller effect.
Finally, we infer a neutron star magnetic field B ~ 4 10^8 Gauss.
