  We propose a fermion Chern-Simons field theory describing two- dimensional
electrons in the lowest Landau level. This theory is constructed with a
complete set of states, and the lowest Landau level constraint is enforced
through a delta-functional described by an auxiliary field lambda. Unlike the
field theory constructed directly with the states in the lowest Landau level,
this theory allows one utilizing the physical picture of "composite fermion" to
study the fractional quantum Hall states by mapping them onto certain integer
quantum Hall states; but unlike it in the unconstrained theory, such a mapping
is sensible only when interactions between electrons are present. An "effective
mass", which characterizes the scale of low energy excitations in the
fractional quantum Hall systems, emerges naturally from our theory. We study a
Gaussian effective theory and interpret physically the dressed stationary point
equation for lambda as an equation for the "mass renormalization" of composite
fermions.
