Washington  - The United States will ask companies to report on their greenhouse-gas emissions that are blamed for global warming, setting the stage for government-imposed limits on climate pollution supported by President Barack Obama and long resisted by his predecessor.

The Environmental Protection Agency (EPA) on Tuesday said it will ask most major polluting firms to submit annual reports on their emissions levels beginning with 2010.

Congress ordered the EPA to set up a monitoring system in 2007, but the initiative was blocked by then-president George W Bush.

The reporting would give the government's climate agency a better understanding of the levels of carbon dioxide produced by the country's top polluters, a key step towards forcing those companies to pay for their emissions.

Obama wants to set up a so-called cap-and-trade system, which already exists in Europe and allocates pollution permits that can be traded between cleaner and dirtier firms.

Such a mandatory limit on greenhouse-gas emissions was rejected by Bush and is still opposed by most Republicans in Congress, especially during the current economic crisis. Most climate groups expect legislation will only be passed in 2010.

EPA Administrator Lisa Jackson called the agency's new reporting requirement a "critical step toward helping us better protect our health and environment."

The rule would apply to about 13,000 facilities that emit between 85 per cent and 90 per cent of the country's greenhouse-gas emissions, the EPA said. Small businesses with low emissions are not covered. (dpa)