The U.S. competitive position in clean energy is lagging, a new report says.

The report, "Innovate, Manufacture, Compete: A Clean Energy Action Plan," released by the Pew Charitable Trusts Thursday says that revenue in the clean energy sector worldwide could total $1.9 trillion from 2012 to 2018.

The United States has the potential to secure 14.5 percent of that revenue, equal to $276 billion, over the next six years, Pew said. But because of uncertainty about government policies for the renewables market, the United States could fail to capitalize on that opportunity.

"U.S. industry has the capacity to be a leader, provided we have the right policies in place," said Phyllis Cuttino, director of Pew's Clean Energy Program, in a release. "It's time for Congress to support a comprehensive energy strategy by delivering long-term certainty for businesses and investors in renewable power."

Pew said roundtable discussions with more than 100 U.S. industry leaders reveal that private investment, manufacturing, and deployment of renewable power have been hampered by the country's lack of a long-term, consistent energy policy.

"Industry is telling us in no uncertain terms that the United States needs to adopt clear, consistent, long-term energy policies that allow American businesses to thrive, make our country more energy secure, and advance environmental imperatives," said Phyllis Cuttino, director of Pew's Clean Energy Program.

Pew recommends an increase in the clean energy tax credit, or Section 48C, to help support the nation's clean energy economy.

To tap into the expected global $6 trillion worth of clean energy investment in the next quarter century, Pew suggests that the U.S. could also focus on exporting technologies, including microgrid and renewable solutions for developing nations with incomplete electric grids.

Among the G20 nations, the U.S. ranks eighth in investment intensity in energy research and development and 10th in the world in installed clean energy capacity growth rate since 2006, the report says.

The nation's competitive position in clean energy is also constrained by tight credit markets, growing international competition and an uneven playing field in fossil energy resources.

"Once a world leader in innovation and manufacturing of clean energy technologies, the United States now faces considerable competitive challenges," the report authors write. "It lags other nations on a variety of measures, including clean energy deployment and manufacturing. Even its long-standing lead in innovation is at risk."

Still, cumulative clean energy installations for non-hydroelectric generation in the U.S. are expected to more than double, reaching 126 gigawatts by 2018, the report says.