In the aftermath of the Disengagement questions regarding rabbinical authority have been raised. In my understanding , in a physical community there should be only one authority, and if there are other rabbis, they must defer to him regarding important questions. The term "gadol hador" sounds a bit pretentious,and each clique uses it for their own chief rabbi, but for arguments sake...... Is there a halachic basis for the "post" of gadol hador, and should the other "chief rabbis" defer to him? Perhaps this is a new order since the creation of the state?
You are correct in your understanding of the authority of the "mara datra"- the rabbi of the community. Since his authority is bestowed upon him by the public that has chosen him, that authority is defined by the community, either explicitly or implicitly. In many instances, the authority of the community rabbi is less today than in the past because of the population's greater mobility. Someone who is a member of one community is likely to move and join another in a few years time only to move on again a few years later. This change has been recognized in the Teshuvot of R' Moshe Feinstein regarding the need to establish a uniform practice within a single community - a need that is less today than in the past. A gadol hador is someone who is accepted as a posek or mentor by large numbers of his fellow-rabbis. In this sense he is similar to an MD whose expertise is recognized by others in his own field, who consult with him when difficult questions arise. His status is based on wisdom and knowledge rather than on official public acceptance of his authority.