The nation's capital is poised to become the first major U.S. city to require private developers to build environmentally friendly projects that help save energy and reduce pollution.

The District of Columbia Council is expected to approve a bill next month that would adopt standards established by the U.S. Green Building Council, which requires "green buildings" to use recycled materials and devices such as low-flow shower heads, toilets and faucets.

The buildings also must have energy-efficient appliances and take steps to improve air quality by relying less on artificial heating and cooling. Sidewalks must be designed to encourage walking and plants must be drought-tolerant.

Going green costs more, however. Proponents say the extra cost of construction ranges from 2 to 4 percent, but opponents say it can cost 11 percent more.

Under the bill, all new city-owned projects, including schools, would have to meet the green standards within two years. By 2012, every new commercial building over 50,000 square feet would have to meet the guidelines.

"This is big," said Cliff Majersik of the Institute for Market Transformation, a nonprofit environmental group that promotes green buildings.

Majersik said smaller cities, such as Pasadena, Calif., have adopted similar laws, but Washington would be the first large city to force private developers to meet the standards.

Bill Hall, a lawyer who represents building material manufacturers, said lobbyists representing some building industry groups are fighting to get communities to use more lenient standards.

"Failure to include these other rating systems would be like the D.C. Council mandating that only Google's search engine can be used in the District to the exclusion of Yahoo and AOL because Google is the most widely used," Hall said.

The Green Building Council has certified 500 buildings in the U.S. as green, and more than 5,000 are awaiting certification, advocates say.

D.C. officials have said the Washington Nationals' new ballpark is being built to green standards.