Gov. Mitt Romney may not get his way on the Northeast climate pact.

A handful of Massachusetts legislators are maneuvering to get their state into the most ambitious U.S. effort yet to fight global warming, the Regional Greenhouse Gas Initiative, launched in late December. If they succeed, it’ll be a smarting wallop for Gov. Mitt Romney (R), who is widely expected to run for a spot on the GOP’s 2008 presidential ticket.

The pact, commonly called RGGI (“Reggie”), commits seven Northeastern states — Connecticut, Delaware, Maine, New Hampshire, New Jersey, New York, and Vermont — to reducing their carbon dioxide emissions 10 percent by 2019. Massachusetts was supposed to be among them, but in mid-December Romney abruptly pulled the state out — despite the fact that several staffers in his administration had spent two and a half years and more than half a million dollars negotiating and shaping the deal. Rhode Island Gov. Donald L. Carcieri (R), an ally of Romney’s, quickly followed suit.