  The decoupling properties of the Higgs sector in the Minimal Supersymmetric
Standard Model (MSSM) imply that a light CP-even Higgs boson discovered at the
Tevatron or LHC may closely resemble the Standard Model (SM) Higgs boson. In
this paper, we investigate how precision measurements of Higgs properties at a
Linear Collider (LC) can distinguish between a CP-even Higgs boson of the MSSM
and the SM Higgs boson. We review the expected theoretical behavior of the
partial widths and branching ratios for decays of the neutral MSSM Higgs bosons
with significant couplings to the W and Z bosons, including the leading
radiative corrections to the mixing angle alpha and tan beta-enhanced vertex
corrections. The general expectation is that the Higgs couplings to W+W-, ZZ, c
cbar and t tbar should quickly approach their SM values for increasing CP-odd
Higgs mass mA, while the couplings to b bbar and tau+ tau- do so more slowly.
Using the expected experimental and theoretical accuracy in determining SM
branching ratios and partial widths, we demonstrate the sensitivity of
measurements at the LC to variations in the MSSM parameters, with particular
attention to the decoupling limit. For a wide range of MSSM parameters, the LC
is sensitive to mA ~ 600 GeV almost independently of tan beta. For large values
of tan beta and some specific choices of MSSM parameters [e.g., A_t mu < 0 and
|A_t| ~ |mu| ~ O(M_S)], one of the CP-even Higgs bosons can be SM-like
independent of the value of mA. In the case of large deviations from the SM, we
present a procedure using Higgs coupling measurements to extract the
supersymmetric correction to the relation between the b quark mass and Yukawa
coupling.
