  Let k be a global field of characteristic not 2. The classical
Hasse-Minkowski theorem states that if two quadratic forms become isomorphic
over all the completions of k, then they are isomorphic over k as well. It is
natural to ask whether this is also true for G-quadratic forms, where G is a
finite group. In the case of number fields the Hasse principle for G-quadratic
forms does not hold in general, as shown by Jorge Morales. The aim of this
paper is to study this question when k is a global field of positive
characteristic. We give a sufficient criterion for the Hasse principle to hold,
and also counter examples : note that these are of different nature than those
for number fields.
