The abelianization of gauge algebras for general models with first-class constraints is considered at the classical level. An explicit ansatz for the abelian constraints is proposed. It is shown that under comparatively weak conditions, this ansatz will solve the problem of abelianization. The finite canonical transformation, which relates the corresponding BRST charges, is discussed and is explicitly constructed for the case of a general Lie algebra. As examples, we treat the models of a scale-invariant point particle, bosonic string and pure Yang-Mills.