Republican gains in the next Congress will likely curtail spending on green construction projects, but the sector promises to be a source of job growth for an economy that sorely needs it, advocates say.

“America needs 30 million jobs. Our mission ought to be to make those green jobs,” David Foster, executive director of the BlueGreen Alliance, a coalition of nine labor unions and four environmental groups, told the Greenbuild Expo in Chicago.

Foster predicted that Republican gains in the Nov. 2 election mean there will be little government investment in green projects next year. But the year after that, Americans will still be clamoring for jobs, and government will have to act, he said.

A study done for the U.S. Green Building Council, organizer of the trade show, estimated that green construction projects had created 2.4 million American jobs between 2000 and 2008.

The Booz Allen Hamilton study projected green building projects will support or create 7.9 million jobs between 2009 and 2013 and will contribute $554 billion to the U.S. gross domestic product.

Weatherization of existing buildings, rehabilitation of older buildings to save energy, renewable energy projects, and a host of other green construction efforts would all be a source of jobs, Foster and other advocates said.

The nearly exhausted federal stimulus program included $80 billion in funding to promote a “green energy economy” and had been effective, Foster said.

“There’s a great record of job creation (with green projects). The problem is you can’t do it just once in a little package. These are big, long-term investments,” Foster said.

China has generated a million green jobs in the past five years, and Foster said it had overtaken the United States in solar and wind energy.

“China’s going to steamroll us if we don’t get into the game,” he said.

Foster expressed regret that the newly elected Republican governor of Wisconsin had promised to halt funding for a high-speed rail project. And New Jersey’s governor halted a project to build another train tunnel between his state and New York City.

Locating the trade show in Chicago seemed apropos. Chicago has more building projects — 40 — certified under the Leadership in Energy and Environmental Design (LEED) and more space devoted to green roofs than any other U.S. city, a spokesman said.