Washington - Carbon dioxide will soon be declared a dangerous pollutant - a move that could help propel slow-moving climate-change legislation on Capitol Hill, the head of the Environmental Protection Agency said Monday.

    EPA Administrator Lisa Jackson told reporters that a formal "endangerment finding," which would trigger federal regulations on greenhouse gas emissions, probably would "happen in the next months."

    Jackson announced her timeline even as top senators said they were delaying plans to introduce legislation that would set new limits on carbon dioxide emissions. Senators had been scheduled to unveil legislation next Tuesday, but the date has now been pushed back to later in September.

    The House narrowly passed a broad energy and climate-change bill in June, but supporters have moved more slowly in the Senate, where the issue has been trumped recently by work on the health care overhaul.

    The EPA kick-started the regulatory process in April when it proposed declaring carbon dioxide and five other greenhouse gases as pollutants that jeopardize the public health and welfare. EPA scientists believe the greenhouse gases contribute to global warming by trapping heat in the Earth's atmosphere.

    The EPA can formalize the finding anytime, now that it has closed a 60-day public comment period that netted more than 300,000 responses.

    A formal endangerment finding would obligate the agency to regulate greenhouse gas pollution under the Clean Air Act - even if Congress doesn't pass a final climate-change bill.

    President Obama and Jackson have said they would prefer that Congress - rather than the EPA - take the lead in implementing new greenhouse gas limits. Businesses and energy industry leaders also have largely favored congressional action over EPA-imposed limits, because they believe lawmakers are better positioned to combine economic safeguards with any new carbon cap.

    "Legislation is so important, because it will combine the most efficient, most economy-wide, least costly (and) least disruptive way to deal with carbon dioxide pollution," Jackson said. "We get further faster without top-down regulation."

    But Jackson insisted the EPA would continue on a path that began when the Supreme Court ruled in 2007 that greenhouse gases qualified as pollutants and could be regulated if the government determined they threatened the public.

    "Two years is a long time for this country to wait for us to respond to the Supreme Court's ruling," Jackson said.

    Supporters of climate change legislation are hoping the threat of EPA-mandated limits will spur congressional action.

    Sens. Barbara Boxer, D-Calif., and John Kerry, D-Mass., had been planning to introduce their own climate change bill next week. But in a joint statement Monday, the pair said they were delaying the bill introduction until "later in September" because of the death of Sen. Edward Kennedy, D-Mass., Kerry's hip surgery in August, and Kerry's membership on the Finance Committee, which is negotiating health care.

    Sen. James Inhofe of Oklahoma, the top Republican on Boxer's Environment and Public Works Committee, said the delay "is emblematic of the division and disarray in the Democratic Party over cap-and-trade and health care legislation."