Sen. John Thune of South Dakota appears likely to inherit the top-ranking Republican seat on the Senate Commerce, Science and Transportation Committee.

Jim DeMint of South Carolina had been expected to assume that job when the new Congress convenes, but he announced Thursday he will leave Congress in January to head a conservative think tank. The top two Republicans on the panel currently — Kay Bailey Hutchison of Texas and Olympia J. Snowe of Maine — are retiring.

Thune, chairman of the Senate Republican Conference, is the next in line in seniority. He made clear Thursday he wants the post. “Of course I am interested in it,” he said.

Hutchison said, “He’s certainly well-regarded, so unless he has another option, I would assume it would be John.”

DeMint, an uncompromising conservative whose aversion to new regulation and government spending made him a tea party favorite, had been expected to set a more combative tone on the committee than Hutchison, the current ranking member.

DeMint has been at odds with infrastructure advocates who want to expand federal funding for road, transit, rail and airport projects.

One lobbyist who works on infrastructure issues said Thune “appears to have a broader perspective and we’ve seen his good hand in bipartisan efforts.”