Washington — A group of Democratic senators is calling for the Interior Department to halt future Alaska offshore drilling leases, saying the president hasn’t made the case that drilling in the environmentally sensitive region is safe.

“Challenges with infrastructure and spill response are unprecedented in the Arctic’s remote, undeveloped region,” the senators wrote Interior Secretary Ken Salazar.

Senators signing the letter this week were Richard Durbin of Illinois, Barbara Boxer of California, Frank Lautenberg of New Jersey, Patrick Leahy of Vermont, Jeff Merkley of Oregon and Sheldon Whitehouse of Rhode Island. They questioned the oil spill response capabilities in the Arctic and said there needs to be a better scientific monitoring plan. They also want more areas off limits.

The senators urged the Interior Department to remove Arctic offshore drilling from its 2012-2017 leasing program. An Interior Department spokesman had no response to the letter on Wednesday.

The Obama administration’s proposed offshore oil leasing program includes a pair of potential sales in the Alaska Arctic. That would be a 2016 sale in the Chukchi Sea and a 2017 sale in the Beaufort Sea.

“We are committed to moving forward with leasing offshore Alaska, and scheduling those sales later in the program allows for further development of scientific information on the oil and gas resource potential in these areas and further study of potential impacts to the environment,” Deputy Interior Secretary David Hayes said when the plan was announced in July.

There’s an intensifying global push to harvest the vast energy resources in Arctic waters, from Alaska to Russia to Greenland.

It’s hugely controversial, and the French oil company Total on Wednesday became the first major driller to speak out against oil exploration in Arctic waters. The company’s chief executive told the London-based Financial Times that the risk of a spill in a sensitive offshore Arctic area such as Greenland was too great.

There’s already preliminary drilling by Shell on existing leases in the Arctic waters off Alaska. The Obama administration gave Shell approval to drill shallow holes but not to go deep enough to actually hit oil. Shell had hoped to reach oil-bearing geological formations this year but gave up on that last week when its oil spill containment dome was damaged during testing off Washington state.

Shell plans to do what shallow drilling it can in the Arctic this fall and resume its efforts after sea ice is gone next year. Salazar has said Shell won’t get permission to go into oil-bearing formations until its spill response equipment is ready.

Shell has been slowed by delays getting its oil spill response barge ready. But Salazar said last week that Shell has shown a commitment to meeting his department’s “rigorous safety, environmental protection and emergency response” standards for the Arctic.

Alaska Sen. Lisa Murkowski, the ranking Republican on the Senate Energy and Natural Resources Committee, says President Barack Obama isn’t going far enough in allowing Arctic drilling.

“The United States has the highest environmental standards and protections in place for offshore drilling,” said Robert Dillon, a spokesman for Murkowski. “And those have been strengthened since the Deepwater Horizon and certainly strengthened even further for Arctic drilling.”

Dillon said Wednesday that the Obama administration plan doesn’t even guarantee there will be offshore leases in the Arctic over the next five years. Murkowski is pressing for guaranteed annual lease sales in both the Chukchi and Beaufort seas. She’s introduced a bill that would allow more sales off Alaska as well as the mid-Atlantic coast and exploration from existing rigs off southern California.

Murkowski’s bill also would give states money from energy production off their coasts and has co-sponsors who include both of Virginia’s Democratic senators, Jim Webb and Mark Warner.