  The thesis gave a fine study on the distribution of the coefficients of
automorphic L-functions for GL(m) with m>1. In particular we have treated two
types of problems: change of signs of these coefficients (when they are real)
and their decompensation on the prime numbers. Chapter 2 is devoted to the
results known concerning the first problem in the case of classical modular
forms and to explain our motivation of research. In Chapter 3, we treated the
case of primitive Maass forms and obtained an estimate of the subconvexity-type
for the least integer n such that the n-th coefficient is negative. Chapter 4
is the main part of the thesis. For the coefficients of the L-function
associated with an irreducible unitary cuspidal representation for GL(m) with
m>1, we established an elegant inequality of Hecke type, which shows that these
coefficients on the first m powers of an arbitrary unramified prime number
cannot be small simultaneously. As an application, we obtained a polynomial
type estimate for the least integer n such that the n-th coefficient is
negative. In Chapters 5 and 6, we studied the long and short summations of
coefficients of L-functions for GL(m) on the prime numbers to test their
decompensation, respectively. In particular we gave a perfect generalization of
Selberg's normal density theorem when m>1.
