By Michelle Nichols

NEW YORK (Reuters) - Investments in energy-saving building retrofits and clean-energy projects can create hundreds of thousands of jobs and bolster the U.S. economy, former U.S. President Bill Clinton said on Tuesday.

More than 1,200 people, including over 50 heads of state such as President Barack Obama, business leaders, humanitarians and celebrities were due to attend the seventh annual Clinton Global Initiative that began on Tuesday.

With the United States possibly tipping into another recession and the unemployment rate at more than 9 percent, Clinton trumpeted a pledge by the AFL-CIO labor federation and the American Federation of Teachers to reinvest $10 billion over the next five years in energy-efficient infrastructure.

"This is a huge deal. This could be done not just in the United States but in every European country, in every wealthy Asian country. This system will work and you get guaranteed savings," Clinton told attendees during the opening session.

Aside from clean energy projects such as wind and solar power, Clinton said pension funds and banks should invest in giving green make-overs to buildings, from hospitals and schools to government buildings. The cost of retrofitting would be paid back by the monthly savings in energy costs, he said.

In cities such as London and New York, buildings are responsible for nearly 70 percent of greenhouse gas emissions. Scientists say heat-trapping gases cause global warming, which could cause deadly floods, droughts and heat waves.

"This (commitment) goes right at the biggest unemployment problem we have in the United States, right at the climate-change challenge and puts more disposable income into the hands of people who will almost certainly spend it," Clinton said.

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Clinton said if American banks started investing some $2 trillion in cash they were sitting on, then "We would have a million jobs in no time."

"This is not rocket science," said Clinton, who began his philanthropic initiative out of his frustration while president between 1993 and 2001 at attending conferences that were more talk than action.

In an effort to jump-start the stalled U.S. economy, Obama introduced a $447 billion plan to create jobs earlier this month. Job growth is crucial to Obama's re-election hopes next year because he is being criticized for the stubbornly high unemployment rate.

To attend Clinton's summit, commitments must be made. If pledges are not kept, you cannot return.

Among pledges announced on Tuesday, Archbishop Desmond Tutu of South Africa, former Irish President Mary Robinson, the Ford Foundation and the NoVo Foundation (run by investor Warren Buffett's son Peter and his wife Jennifer) announced a global partnership to end child marriage.

In poor countries, one in three girls is married before 18, they said, ending their schooling and exposing them to abuse. The group wants to wipe out the practice in a generation.

"I'm going to be as committed to it as I was to ending apartheid," Nobel Peace Prize laureate Tutu told reporters.

Since its inception, the Clinton Global Initiative has yielded more than 2,000 pledges valued at more than $63 billion, which have improved the lives of more than 300 million people in 180 countries, organizers say.

(Editing by Mark Egan and Philip Barbara)