LAS VEGAS — Former Secretary of State Hillary Rodham Clinton said Thursday the U.S. should become what she called the world's 21st-century clean energy superpower, during remarks resembling both a campaign speech and a call to action at the annual National Clean Energy Summit in Las Vegas.Clinton cast the threat of global climate change as real, and "the most consequential, urgent, sweeping collection of challenges" faced by the nation and the world."The data is unforgiving," the former New York senator and first lady said to a standing room crowd of more than 800 people at a Las Vegas Strip resort. "No matter what the deniers try to assert. Sea levels are rising. Ice caps are melting. Storms, droughts and wildfires are wreaking havoc.""The threat is real but so is the opportunity," she said.Clinton, widely considered a leading Democratic candidate for president, used her speech to plug her book, "Hard Choices," and the work of the Clinton Climate Initiative arm of a foundation founded in 2005 by her husband, former President Bill Clinton.She also segued into the topic of the day at the seventh annual green energy conference hosted by U.S. Senate Democratic Majority Leader Harry Reid.Clinton credited northern Nevada's selection for a $5 billion Tesla automobile battery plant to the emergence of Nevada as a leader in solar, wind and geothermal energy projects.She also cited a quote by Robert Lang, director of Brookings Mountain West, at the University of Nevada, Las Vegas, comparing the promised investment in the Tesla plant near Reno to the importance of the 1930s Hoover Dam project on the Colorado River east of Las Vegas."Nevada was competitive because it had already invested in green energy, solar, geothermal and wind," Clinton said.Clinton's speech to a standing-room crowd of more than 800 marked her return to the Las Vegas Strip hotel where a 36-year-old Phoenix woman was arrested in April after throwing a shoe but missing Clinton on stage. Security was tight, with federal agents and local police visible, and there was no similar disruption on Thursday.Once, Clinton referred to the 112 countries she said she visited as secretary of state.She said she came away optimistic about what the U.S. can do "when we decide we're in the futures business in America.""If we come together to make the hard choices, the smart investment in infrastructure, technology and environmental protection, America can be the clean energy superpower for the 21st century," she said.A focus on the Tesla plant upstaged an earlier announcement that a northern Nevada biofuel production plant would receive a federal loan guarantee for a little under 40 percent of its $266 million cost.Reid and federal Agriculture Secretary Tom Vilsack joined Fulcrum Sierra BioFuels chief executive E. James Macias as he declared his project ready for construction by the end of the year and touted military uses for the estimated 10 million gallons of diesel, maritime and jet fuel it is expected to produce by 2016.Vilsack said the U.S. Department of Agriculture was backing a $105 million loan.The Sierra BioFuels Plant will be a neighbor with Tesla in the same industrial park in Storey County.Reid noted that Tesla CEO Elon Musk spoke two years ago at the conference about the importance of innovation and investment in clean energy, and recalled that Tesla benefited four years ago from a $465 million federal Department of Energy loan that helped it build a manufacturing plant in California."Tesla is the company it is today because of this loan," Reid said.Reid also said Nevada's efforts to lure the Tesla plant benefited from a ready supply of lithium for battery production. He pointed to a $28.4 million Energy Department grant in 2010 to Rockwood Lithium for a lithium carbonate and lithium hydroxide plant in Silver Creek, Nevada.Amory Lovins, co-founder and chief scientist at the Rocky Mountain Institute in Colorado, and one of the nation's most influential energy thinkers, said after a conference presentation that he expected the Tesla factory would benefit both Nevada and the company."People have not made money by betting against them so far," Lovens said of the upstart carmaker, where he said he had friends, and which he said he visited a couple of weeks ago."They've hired very experienced people who have been running car factories all their lives to do it," Lovins said, "and they've done it extremely well."