Many people who know P. Leonardo Mascheroni describe him as a maverick and a technology zealot. Now, the Justice Department will try to prove that he is dangerous, too -- a man willing to sell atomic secrets in exchange for a chance to realize his dream. Mascheroni, 75, is a nuclear scientist who has spent the 22 years since he left the Los Alamos National Laboratory trying to sell Congress, the scientific community, journalists -- anyone who would listen, really -- on his plan to build a giant laser for the achievement of nuclear fusion. His plan earned respect and high-level endorsements, but the government chose a different path. Rather than give up, Mascheroni redoubled his campaign, sending out lengthy technical documents from his home in New Mexico to try to coax Washington to finance his laser. As he was snubbed by Congress and federal experts, Mascheroni, a naturalized citizen who was born in Argentina, grew increasingly frustrated and bitter. He became known in Washington for veiled threats to take his atomic expertise abroad unless the government backed his laser plan. He seemed to think that he could bully the federal establishment into big spending, according to people on the receiving end of his missives. 'He came at you like a force of nature,' recalled Matthew G. McKinzie, a former Los Alamos researcher who is now at the Natural Resources Defense Council, a private group in Washington. 'He and his coterie of followers at Los Alamos believed his approach could provide a source of limitless, clean energy for humanity.' A 22-count indictment against Mascheroni, made public Sept. 17, quotes his wife, Marjorie, as saying that he would 'make bombs' overseas 'if they don't listen to him in Washington.' She has been charged as a co-conspirator, and both of them have pleaded not guilty. 'If I were a real spy, I would have left the country a long time ago,' Mascheroni said. Federal prosecutors have charged Mascheroni with trying to sell nuclear secrets to Venezuela as part of a complicated scheme to have that country bring his laser to life. According to the indictment, he negotiated a deal in 2008 and 2009 with an undercover FBI agent, who paid him $20,000 out of an overall promise of nearly $800,000. The laser that Mascheroni wants to build could provide -- in theory -- an unusual but potentially limitless source of energy for the world, and in particular for the United States, his adopted home. 