WASHINGTON, Sept 9 (Reuters) - The United Steelworkersunion on Thursday asked President Barack Obama's administrationto investigate Chinese policies and practices it saidthreatened to unfairly take U.S. clean energy jobs.

"Green jobs are key to our future," Leo Gerard, presidentof the steelworkers union, said in statement.

"Right now, China is taking every possible step -- many ofthem illegal under international trade laws -- to ensure thatit will control that sector. America can't afford to cede moreof its manufacturing base to China," Gerard said.

The case comes at a time when Obama has touted thepotential for new jobs in wind, solar and other clean energysectors as an engine for U.S. economic growth.

The steelworkers said they filed a formal "section 301"petition with the U.S. Trade Representative's office onThursday, asking for an investigation of "China's illegalactivities in five key areas."

The union accused China trying to dominate the clean energysector by providing billions of dollars in trade-distortingdomestic subsidies, using prohibited export subsidies andprohibited domestic content subsidies, discriminating againstforeign firms and goods, restricting access to criticalmaterial and imposing performance requirements on investors.

Tom Conway, the union's vice president, said the UnitedStates is losing its leadership in the clean-energy sector "inlarge part because of China's plans to control this industry nomatter what. They're breaking every rule in the book."

A spokeswoman for the USTR said the agency would review thepetition "in accordance with established procedures" and make adecision whether to investigate within 45 days.

Also, U.S. Commerce Secretary Gary Locke led a trademission of nearly two dozen U.S. companies to China in May totry to boost sales in that country's renewable energy marketwhich has been forecast to reach $100 billion by 2020.

Last October, Locke and U.S. Trade Representative Ron Kirkgot a high-level Chinese commitment to remove local contentrequirements for foreign participation in China's wind farmmarket, which they said would boost U.S. jobs.

The steelworkers said they were unimpressed by pledges ofU.S.-China cooperation on the clean energy front.

"We can't rely on unending diplomatic niceties andnon-productive photo opportunities masquerading as serioustalks," Gerard said. "We're hemorrhaging jobs, seeing ourbilateral trade deficit skyrocket and jeopardizing ourfuture."

(Reporting by Doug Palmer; Editing by Bill Trott)