Gov. Chris Christie said Thursday that New Jersey would become the first state to withdraw from a 10-state trading system, the Regional Greenhouse Gas Initiative, declaring it an ineffective way to reduce carbon dioxide emissions.

The decision delighted Republicans who have introduced bills in the New Jersey Legislature to repeal a law authorizing the state’s participation in the program. But it dismayed environmental advocates, who called it a serious blow to the state’s efforts to reduce emissions from power plants and foster a shift from fossil fuels to renewable energy.

Opponents were quick to ascribe political motives to the governor’s decision, given that Mr. Christie is seen as a possible Republican candidate in the 2012 presidential race and conservatives have vilified cap-and-trade programs, which set limits on emissions, as an unjust tax on business. (Mr. Christie insists he is not running.)

At a morning news conference, the governor asserted that New Jersey was succeeding in reducing its carbon dioxide emissions not because of the multistate program, known as RGGI (pronounced Reggie), but because it is relying more on natural gas and less on coal to fill its energy needs.