The study of hot plasma expansion in a uniform magnetic field is of interest for many astrophysical applications. In order to observe this process in laboratory, an experiment is proposed in which an ultrashort laser pulse produces a high-temperature plasma by irradiation of a jet of atomic clusters. The very high laser light absorption exhibited in such a gas of clusters facilitates the creation of a hot (> 5 keV), dense (10(19)-10(20) cm(-3)) plasma with a sharp boundary. The small scale of the plasma (<100 mu m radius) permits the use of a strong magnetic field (> 1T). Pump-probe techniques can then be used to diagnose the density and magnetic field with high spatial and temporal resolution (<50fs). In the present work the expansion rate of the plasma and deceleration caused by the magnetic field are examined analytically. Electrodynamical aspects related to the radiation and transformation of energy are considered as well. The results obtained can be used in treating experimental data, studying magnetic R-T instabilities and other phenomena of astrophysical significance.