Lutz filtration as Galois module in an extension without higher ramification

One considers the structure of the group of the points of a formal group and its Lutz filtration as a Galois module in an extension without higher ramification of a local field. Making use, on one hand, of Honda's theory on the classification of formal groups over complete local rings and, on the other hand, of a generalization to formal groups of the Artin-Hasse function, one constructs effectively an isomorphism between the group of points and some given additive free Galois module. In particular, in the multiplicative case one gives a new effective proof of Krasner's theorem on the normal basis of the group of principal units of a local field in extensions without higher ramification.