Constellation Energy said Saturday that it had reached an impasse in negotiations for a federal loan guarantee to build a proposed third nuclear reactor at its Calvert Cliffs site near Washington. The decision would appear to kill the project unless Congress or the White House steps in. Constellation said in a letter to the Energy Department that the Office of Management and Budget was asking for a fee of $880 million on a guarantee of about $7.6 billion, which it said would doom the project, 'or the economics of any nuclear project, for that matter.' The fee is to compensate taxpayers for the risk of default. The company argues that because the plant's model is being proven in Finland, France and China, and because it has a strong partner, Electricite de France, the fee should be 1 to 2 percent. The Calvert Cliffs project had once been hailed as a cornerstone of a nuclear power renaissance. In 2005, President George W. Bush spoke at Calvert Cliffs, the first presidential visit to a nuclear plant in 30 years. 'It is time for this country to start building nuclear power plants again,' he said. The last successful groundbreaking for a nuclear reactor in the United States was in 1973. The federal government authorized a loan guarantee program in 2005 intended to spur nuclear power development, and Congress agreed to finance it in 2007. So far, however, only one guarantee has been issued, for two new units at the Southern Co.'s Vogtle plant, near Waynesboro, Ga. Ground has been broken there, and also for two more reactors across the Savannah River in South Carolina, a project that is proceeding without loan guarantees. But a variety of utilities around the country have stepped back from plans to build reactors. Constellation, which serves a large area of Maryland and owns generating plants nationwide, announced its decision Saturday after the impasse was reported by The Washington Post. On Saturday, James L. Connaughton, executive vice president of Constellation and an environmental official in the Bush White House, stopped short of saying the project was dead. 'We were in the middle of discussions,' he said. The government had proposed a lower fee if Constellation agreed to buy three-quarters of the power and Constellation and EDF guaranteed completion of the plant, said Connaughton, but he said those conditions were too onerous. In a statement, EDF said it was 'extremely disappointed and shocked to learn that Constellation has unilaterally decided to withdraw from the Calvert Cliffs 3 project.' 