A top U.S. Fish and Wildlife Service official has determined that the Delta smelt should be listed as a species "threatened" by extinction, rather than "endangered." The distinction, which overrules a proposal made by lower-ranked officials, would extend less protection to the small fish. Explaining his conclusion in a two-paragraph memo, Deputy Director Richard Smith said the smelt's population has been "relatively stable" for five years. The agency has not issued a final decision on the smelt, which is found only in the Sacramento-San Joaquin River Delta.