  The fluctuating diamagnetic magnetization Mfl at constant field H as a
function of temperature and the isothermal magnetization Mfl vs H are measured
in MgB2, above the superconducting transition temperature. The expressions for
Mfl in randomly oriented powders are derived in the Gaussian approximation of
local Ginzburg-Landau theory and used for the analysis of the data. The scaled
magnetization Mfl/H^{1/2}*T is found to be field dependent. In the limit of
evanescent field the behaviour for Gaussian fluctuations is obeyed while for
H>~ 100 Oe the field tends to suppress the fluctuating pairs, with a field
dependence of Mfl close to the one expected when short wavelength fluctuations
and non-local electrodynamic effects are taken into account. Our data, besides
providing the isothermal magnetization curves for T>Tc(0) in a BCS-type
superconductor such as MgB2, evidence an enhancement of the fluctuating
diamagnetism which is related to the occurrence in this new superconductor of
an anisotropic spectrum of the superconducting fluctuations.
