Piggybacking on a renewed national focus on global warming, the City Council is looking to enact a far-reaching bill that would impose ambitious targets for the city to reduce its emissions of greenhouse gases by 2020.

The New York City Climate Protection Act would mandate a 25% cut in emissions of carbon dioxide from government operations by 2015 and a 30% reduction by 2020. The bill also would require the city to conduct an inventory of emissions from nongovernment activities, as well as to devise a program to encourage private businesses and organizations to reduce pollution stemming from their operations.

The bill comes as officials said yesterday that the city has surpassed international goals set by the Kyoto Protocol, but is well behind its own target of a 20% reduction in the 15-year period ending in 2010.

The council measure does not yet have the support of the Bloomberg administration. In testimony at a hearing yesterday, the director of the Office of Environmental Coordination, Robert Kulikowski, said the legislation “oversimplifies a very complex issue.”

Despite the differences over the bill, there is no debate between the council and the mayor about global warming, and little question that the city must curb its potential effects. In a speech last month at Johns Hopkins University, Mayor Bloomberg warned that “despite near unanimity in the science community, there’s now a movement – driven by ideology and short-term economics – to ignore the evidence and discredit the reality of climate change.”

The bill makes no requirements of non-city operations or private businesses, sidestepping the controversial issue of government regulation. Mr. Kulikowski, however, said businesses would not be a hard sell, that “the private sector is really chomping at the bit to start using green technology.”

The chairman of the council’s Committee on Environmental Protection, James Gennaro, introduced a similar bill last year. He is pressing ahead with his legislation as the national spotlight has returned to climate change with the recent release of “An Inconvenient Truth,” a documentary featuring Vice President Gore arguing the case for the existence of global warming.

The film was mentioned several times at yesterday’s hearing, but Mr. Kulikowski cautioned Mr. Gennaro not to overreach. “While it is important to act locally,” he said, “we must place this local action into the global context and not fool ourselves into thinking that by acting in New York City we will solve the problem.”

At issue in the council’s bill is the amount of carbon dioxide pumped into the atmosphere by city-run buildings, vehicles, streetlights, water, and waste. An early analysis of data shows that the city is on pace to reduce its emissions by 12% by 2010 over 1995 levels. The city had set 20% as a goal for 2010, but Mr. Kulikowski said that once the city completes its analysis later this year, it may revise that target to a more realistic number.

Mr. Kulikowski said the city has not estimated what it would cost to make city operations efficient enough to accommodate the bill’s requirements, but that the city could ultimately save money if the changes are effective. He said the city was taking other steps to counteract greenhouse gas emissions, such as planting more trees, reducing the miles traveled by city vehicles, and increasing their fuel efficiency.