WASHINGTON — The government will start keeping track of all the "greenhouse" gases that farmers and foresters voluntarily reduce to help combat global warming.

Officials in the Energy and Agriculture departments issued guidelines Wednesday for counting those efforts. They said the action indicates how seriously the Bush administration views the problem of gases that trap heat in the atmosphere like a greenhouse.

Agriculture Secretary Mike Johanns said farm and forest landowners now have "a unique opportunity to be part of the solution to greenhouse gas emissions" such as carbon dioxide, methane, nitrous oxides, refrigerants and other compounds.

For example, they can report using no-till agriculture, installing a waste digester, improving nutrient management or managing forest land in ways that cut those gases.

The Forest Service and Natural Resources Conservation Service also have prepared an online method for farmers and ranchers to estimate soil carbon sequestration — the natural process by which carbon dioxide in the air is turned into carbon stored in soil and plants.

Since 1992, the United States has kept a registry of voluntary efforts by businesses, groups and individuals to reduce greenhouse gases. Doing so helps build a public record for policymaking and negotiations with other countries.

David Hawkins, director of Natural Resources Defense Council's climate center, called the reporting registry a "charade that is intended to allow the government and the participants to portray that they are doing something about global warming, when they are not."

For example, companies running nuclear reactors can claim greenhouse gas reductions by saying they would have otherwise operated coal-fired power plants, Hawkins said.

In another case, Hawkins said, one coal-fired power plant in Maryland claims reductions for selling some of its carbon dioxide to the food and beverage industry, even though the carbon dioxide is eventually released anyway once a drink is opened and consumed.

"To call it a reduction is absurd, but the Department of Energy allows them to file it as a report and call it a reduction," Hawkins said.

In 2003, the Agriculture Department said it would start rewarding farmers and ranchers whose tilling and planting practices help reduce greenhouse gases by increasing carbon sequestration. It was not clear whether those rewards are linked in any way to the voluntary reporting.

Carbon sequestration is regarded as a way of slowing the growth in greenhouse gases but not by itself a solution to global warming.