????Former president tells leading figures in renewable energy business to make the technology competitive on cost - and calls for heavier government support.

????By Steve Hargreaves

????Former President Bill Clinton urged renewable energy Wednesday to push ahead with efforts to make clean technologies cost effective and outlined steps the government and the private sector can take to usher in a new green era.

????"The most important thing you can do is to prove that the transformation can be good economics," Clinton said in a keynote speech capping Fortune's Brainstorm Green conference, which drew a mostly corporate crowd from firms big and small.

????Making clean energy cost effective is important in popularizing the technology, but it would also counter criticism from those who say global warming is not a major threat, said Clinton.

????Clinton highlighted the current recession and the economic challenges that it posed, but also said the nation should take advantage of the economic stimulus act to invest even more heavily in clean technology. He noted that China is doing just that: When measured as a percentage of its economy, China is engaged in a larger stimulus effort than is the United States.

????"This thing will work itself out," Clinton said of the deep recession. "The only way for us to come out of this in a better way than we went in is to change the way we produce and consume energy."

????To shepherd that change, Clinton said, the federal government should extend renewable energy tax credits, invest more money in building a better electric and do more to create a bigger market for hybrid and electric cars.

????On the corporate side, he said efforts like those Wal-Mart has made to reduce packaging have had a big effect on cutting pollution. Clinton also urged more widespread construction of green buildings and a greater effort to organize financing.

????He highlighted projects that his own foundation is working on to improve the environment, along with a partnership of 40 cities worldwide, including recovering methane from landfills in Mexico City, improving traffic flow in Seoul and making New York buildings more energy efficient.

????"For those of us that don't have a vote in Congress or Copenhagen," said Clinton, referring to the upcoming climate talks in Europe, "the most important thing we can do is do."