WASHINGTON — The new Republican Congress is headed for a clash with the White House over two ambitious Environmental Protection Agency regulations that are the heart of President Obama’s climate change agenda.

Senator Mitch McConnell, the next majority leader, has already vowed to fight the rules, which could curb planet-warming carbon pollution but ultimately shut down coal-fired power plants in his native Kentucky. Mr. McConnell and other Republicans are, in the meantime, stepping up their demands that the president approve construction of the Keystone XL pipeline to carry petroleum from Canadian oil sands to refineries on the Gulf Coast.

At this point, Republicans do not have the votes to repeal the E.P.A. regulations, which will have far more impact on curbing carbon emissions than stopping the pipeline, but they say they will use their new powers to delay, defund and otherwise undermine them. Senator James M. Inhofe of Oklahoma, a prominent skeptic of climate change and the presumed new chairman of the Senate Environment and Public Works Committee, is expected to open investigations into the E.P.A., call for cuts in its funding and delay the regulations as long as possible.

The Republicans’ new majority in the Senate also increases their leverage in pushing Mr. Obama to approve the pipeline, although it is still unclear if he will do so.