By Yereth Rosen

ANCHORAGE, Alaska (Reuters) - One of the drill ships that Royal Dutch Shell plans to use in a controversial Arctic drilling program slipped off its moorings and drifted to the edge of shore in Alaska's Aleutian islands, a U.S. Coast Guard representative said on Sunday.

The 500-foot (152-meter) Noble Discoverer, contracted by Shell to drill exploration wells in the remote Chukchi Sea off northwestern Alaska, drifted in windy conditions on Saturday afternoon to within 100 yards of shore in an Aleutian bay, Coast Guard Petty Officer Sara Francis said.

A tug towed the ship back to its mooring site, and the Discoverer was re-anchored, she said, adding that winds were gusting up to 35 mph at the time.

The ship's crew did not feel any shuddering or other indications of impact, Francis said. "It was extremely close to shore. But the initial indications were that the vessel wasn't actually aground," Francis said.

A remotely-operated vehicle inspected the hull on Sunday and found no damage, Francis said.

Shell has sent for divers to inspect the hull "to be sure there's no issue with the integrity" of the ship, Shell spokesman Curtis Smith said. The divers were expected to work over the next few days, he said.

Environmentalists and some Alaska Native groups have been adamantly opposed Shell's Arctic drilling plans, citing risks of oil spills and other accidents in the harsh Arctic environment.

Lois Epstein, Arctic program director for The Wilderness Society, said the Discoverer mishap in relatively sheltered Dutch Harbor bodes ill for operations in the Arctic Ocean.

The Discoverer was 1,000 miles south of its Chukchi Sea destination.

"The conditions in the Arctic are far more harsh, far more extreme," Epstein said. "When you're out in the Arctic, the consequences are enormous when things go wrong."

A local website, the Dutch Harbor Telegraph, reported that the ship bumped the beach near a big hotel. The local public radio station, KUCB, said the ship appears to have run aground. Both news organizations posted photographs on their websites showing the ship nosing the shore.

The Discoverer is among a fleet of ships Shell is amassing to travel to Arctic waters in the next weeks. The company plans to drill up to three exploration wells in the Chukchi and up to two in the Beaufort, off Alaska's northern coast.

The Discoverer's drifting incident is the latest in a series of recent problems encountered by Shell as it prepares to drill exploration wells in Arctic waters this summer.

Plans to start drilling this month have been delayed until August by unexpected thick pack ice, Shell said.

U.S. regulators have required all operations in both the Chukchi and Beaufort seas to stop by October 31. Drilling into hydrocarbon-bearing zones in the Chukchi must cease by late September, making the drill schedule there especially tight.

Shell's Smith said it was unclear whether the company will have the time this year to drill all three wells planned in the Chukchi.

"We're going to have to recalibrate our expectations in the near future and make the most of the time that we do have," he said. But the Discoverer problem in Dutch Harbor was not expected to delay drilling, Smith said.

"The Disco (the ship) is once again moored and taking on supplies in preparation for a late-July departure," he said.

(Editing by Daniel Trotta and Paul Simao)