Officials from the Obama administration have been lobbying China to talk about climate change.

Secretary of State Hillary Rodham Clinton was there in February. House Speaker Nancy Pelosi and other Congressional leaders visited in May. followed by experts from the Energy Department and the White House.

There also has been regular contact at a series of “major economies” meetings that began during the Bush administration and include the 17 biggest emitters of greenhouse gases.

Without the enthusiastic participation of China - and, of course, the United States - negotiations in December in Copenhagen aimed at writing a new global agreement to replace the expiring 1997 Kyoto Protocol are almost sure to fail. The health of the planet is equally at stake. The United States is the largest per capita emitter of greenhouse gases; China is the biggest overall emitter. If they cannot agree on a common strategy, atmospheric levels of carbon dioxide are likely to reach potentially disastrous levels.

Ms. Pelosi found herself greatly encouraged by the dialogue but deeply afraid that the two countries would fall into an old trap: hiding behind each other so that neither would have to do anything difficult or expensive.

It’s a legitimate fear. This dance has to end. True, there have been positive steps on both sides. President Obama has proposed tough new fuel-economy standards and authorized his Environmental Protection Agency to explore controls on greenhouse gas emissions from vehicles, power plants and other industrial sources. China is investing heavily in carbon-free energy sources like wind and solar while trying to clean up its ubiquitous coal-fired power plants.

Yet neither country has really committed to the kinds of reductions that are needed. A bill that seeks a mandatory 80 percent cut in America’s emissions by midcentury has barely begun its journey through Congress. The Chinese, meanwhile, are not even thinking about mandatory limits; they have said they will try to limit “carbon intensity” - the amount of energy emitted per unit of gross domestic product - which is another way of saying emissions will be allowed to rise.

Washington’s leverage over Beijing is not great. Its best option, by far, is to set a positive example: to press ahead with Mr. Obama’s initiatives, to keep investing in cleaner technologies, to enact meaningful legislation. This may not be enough to get the Chinese to do what’s necessary, but it will take away an important excuse.