Hamiltonian formalism with several variables and quantum field theory, PartI

We discuss in this paper the canonical structure of classical field theory in finite dimensions within the {\it{pataplectic}} hamiltonian formulation, where we put forward the role of Legendre correspondance. We define the Poisson $\mathfrak{p}$-brackets and $\mathfrak{\omega}$-brackets which are the analogues of the Poisson bracket on forms. We formulate the equations of motion of forms in terms of $\mathfrak{p}$-brackets and $\mathfrak{\omega}$-brackets with the $n$-form ${\cal H}\omega$. As illustration of our formalism we present two examples: the interacting scalar fields and conformal string theory.