CHICAGO  Mayor Richard M. Daley of Chicago on Thursday unveiled perhaps the most aggressive plan of any major American city to reduce heat-trapping gases.

The blueprint would change the city’s building codes to promote energy efficiency. It also calls for installing huge solar panels at municipal properties and building alternative fueling stations.

Ron Burke, a director with the Union of Concerned Scientists, which helped shape the plan, said it was “more robust and quantitative than those in any other city.”

Like hundreds of other cities, Chicago has pledged by 2020 to reduce the emissions of heat-trapping gases 25 percent from the levels in 1990, the baseline established by the Kyoto Protocol, an international climate treaty. Mr. Burke said the Chicago plan offered much more specific ways than other cities’ plans to measure and cut the emissions.