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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.

The White House vowed to fight back. “We know that there will be attempts to impede or scale back our actions,” John D. Podesta, the senior White House counselor who is leading Mr. Obama’s climate agenda, said in a statement on Monday. But he added, “We’re confident we can prevail.”

For Mr. McConnell, fierce opposition to the E.P.A. regulations is more than just a political priority. Kentucky is one of the country’s top coal producers, and coal generates over 90 percent of the state’s electricity. His re-election campaign was driven by a promise to protect Kentucky from what Republicans called Mr. Obama’s “war on coal.”

“I have heard from Kentuckians across the commonwealth about the pain being inflicted on them by E.P.A.’s unilateral actions,” Mr. McConnell said in a statement. “I fully intend to do everything I can do to fight these onerous E.P.A. regulations.”

Mr. Inhofe has gained headlines throughout his career for asserting that the science of human-caused climate change has been falsified. He is the author of “The Greatest Hoax: How the Global Warming Conspiracy Threatens Your Future.” But while Republicans may be able to muster enough of a majority to pass bills that would block or delay the climate rules, it is a near certainty that Mr. Obama would veto such legislation. And Mr. McConnell could not gather the two-thirds majority in the Senate necessary to override a presidential veto.

Still, both Mr. McConnell and Mr. Inhofe are seasoned veterans of congressional procedure, willing and able to deploy a range of tactics designed to slow or hamstring the rules.

Mr. McConnell signaled last week that he, too, wanted to cut the E.P.A.’s budget to keep it from enforcing environmental regulations. Republicans might also include provisions that would repeal the E.P.A. regulations in crucial spending bills — a tactic that could force a standoff between Mr. Obama and Mr. McConnell over funding the government.

Mr. Inhofe was also expected to use his environmental committee chairmanship to hold hearings grilling Gina McCarthy, the E.P.A. administrator. As chairman of the committee during the Bush administration, Mr. Inhofe did not hesitate to investigate the environmental policies of his own party. “He was willing to do aggressive oversight during the Bush administration,” said Andrew Wheeler, a former chief of staff for Mr. Inhofe. “This time, it’s going to be very aggressive.”

But some environmentalists said Mr. Inhofe’s assault could backfire politically. “If the Republican Party doubles down on this brand of climate denial, it will go very badly for them,” said David Doniger, a lawyer with the Natural Resources Defense Council, an advocacy group.

Republicans also planned to use their majority to enact legislation requiring the president to approve the Keystone pipeline. Republicans and the oil industry have issued angry calls for construction of the pipeline, which they see as a crucial conduit for oil. Environmentalists have campaigned against the project, which they see as a symbol of environmental degradation. Mr. Obama has delayed a decision on the project for years, as the State Department conducted numerous reviews of its impact on the nation’s environment, economy and national security.

The State Department is now awaiting a decision by a Nebraska court on the route of the pipeline before any decision is made.

If Republicans send a Keystone bill to Mr. Obama before the Nebraska verdict, the president is likely to veto it. But people familiar with the president’s thinking say that when it comes to climate change policy, Mr. Obama sees the E.P.A. regulations as the centerpiece of his environmental agenda and the Keystone pipeline as a sideline issue.

Asked about the project at a news conference last week, Mr. Obama said, “I’m going to let that process play out.” Then he added, “And I’m just going to gather up the facts.”

Republicans were likely to add a Keystone-approval provision to key spending bills, again daring Mr. Obama to veto such a measure. Mr. Obama appeared willing to veto such measures to protect the climate change rules, which could have an impact on the nation’s energy economy for the coming decades. But he may not be willing to do so for the pipeline, a single piece of infrastructure.

“I think there is probably a deal to be had on Keystone,” said David Goldwyn, who led the State Department’s Bureau of Energy Resources in Mr. Obama’s first term. “If Republicans attach Keystone to a budget bill, I don’t think he’s so principally opposed to it that he would veto it.”