  A detailed program is proposed in the Lagrangian formalism to investigate the
dynamical behavior of a theory with singular Lagrangian. This program goes on,
at different levels, parallel to the Hamiltonian analysis. In particular, we
introduce the notions of first class and second class Lagrangian constraints.
We show each sequence of first class constraints leads to a Neother identity
and consequently to a gauge transformation. We give a general formula for
counting the dynamical variables in Lagrangian formalism. As the main advantage
of Lagrangian approach, we show the whole procedure can also be performed
covariantly. Several examples are given to make our Lagrangian approach clear.
