The following theorem is proved. Let

be a binary nonzero polynomial of

variables of degree

. H the number of binary

-tuples

with

= 1 is less than

, then

can be reduced by an invertible affme transformation of its variables to one of the following forms. begin{equation} f = y_1 cdots y_{nu - mu} (y_{nu-mu+1} cdots y_{nu} + y_{nu+1} cdots y_{nu+mu}), end{equation} where

and

. begin{equation} f = y_1 cdots y_{nu-2}(y_{nu-1} y_{nu} + y_{nu+1} y_{nu+2} + cdots + y_{nu+2mu -3} y_{nu+2mu-2}), end{equation} This theorem completely characterizes the codewords of the

th-order Reed-Muller code whose weights are less than twice the minimum weight and leads to the weight enumerators for those codewords. These weight formulas are extensions of Berlekamp and Sloane\´s results.