Factbox: Key 2010 dates for climate debate

WASHINGTON (Reuters) - The U.S. Senate is struggling to find a compromise measure to require industry reductions of carbon dioxide emissions blamed for climate change.

A wide-ranging, complex bill likely would require a long debate in the Senate and anything that passes there would have to be reconciled with a much different bill approved last year by the House of Representatives.

There's no guarantee Congress will be able to finish legislation this year, especially with time dwindling before November elections and other bills taking a higher priority.

Following are some key dates to watch for:

* SOMETIME IN MARCH

The U.S. Environmental Protection Agency could set forth regulations mandating reductions in vehicles' carbon dioxide emissions. It would mark the first time the federal government would regulate carbon and open the way for broader controls on the 6.4 billion metric tons of pollution. Some states and business groups are already challenging EPA's authority to expand its mandate. If a regulation goes ahead, it could put more pressure on Congress to pass legislation that contains lawmakers' preferences.

* MARCH OR APRIL

Senator Lisa Murkowski could try to pass legislation stopping EPA from regulating carbon. She has not yet indicated she has enough votes for passage in the Senate, and the White House says it would work hard to defeat it.

* MAY OR JUNE

Senator John Kerry, who is leading the Senate drive for a climate control bill, says he wants a measure debated and passed by the full Senate this spring. If he can't pull it off by then, the initiative could be doomed this year. By midyear, lawmakers running for re-election will be in full campaign mode, with partisanship even worse than usual and it will be harder for lawmakers to cut deals.

NOVEMBER 2

Election Day. All 435 seats in the House and 38 of the 100 Senate seats are up for grabs in an election that will determine whether Democrats or Republicans hold majority power in each chamber in 2011-2012. Even if Democrats hold on, their majorities could be much smaller, making it even more difficult to pass a comprehensive climate bill.

(Reporting by Richard Cowan; editing by Todd Eastham)