  We present a method to compute the two-point functions for an $O(N)$ scalar
field model in de Sitter spacetime, avoiding the well known infrared problems
for massless fields. The method is based on an exact treatment of the Euclidean
zero modes and a perturbative one of the nonzero modes, and involves a partial
resummation of the leading secular terms. This resummation, crucial to obtain a
decay of the correlation functions, is implemented along with a double
expansion in an effective coupling constant $\sqrt\lambda$ and in $1/N$. The
results reduce to those known in the leading infrared approximation and
coincide with the ones obtained directly in Lorentzian de Sitter spacetime in
the large $N$ limit. The new method allows for a systematic calculation of
higher order corrections both in $\sqrt\lambda$ and in $1/N$.
