WASHINGTON  Officials weighing federal applications by utilities to build new coal-fired power plants cannot consider their greenhouse gas output, the head of the Environmental Protection Agency ruled late Thursday. Some environmentalists fear the decision will clear the way for the approval of several such plants in the last days of the Bush administration.

The ruling, by Stephen L. Johnson, the administrator, responds to a decision made last month by the Environmental Appeals Board, a panel within the E.P.A., that had blocked the construction of a small new plant on the site of an existing power plant, Bonanza, on Ute tribal land in eastern Utah.

The Supreme Court ruled last year that the agency could regulate carbon dioxide, the most prevalent global warming gas, under existing law. The agency already requires some power plants to track how much carbon dioxide they emit.

But a memorandum issued by Mr. Johnson late Thursday puts the agency on record saying that carbon dioxide is not a pollutant to be regulated when approving power plants. He cited “sound policy considerations.”