WASHINGTON – Shell is giving up for the year on drilling for oil in the offshore Alaskan Arctic after an accident damaged its oil spill-containment dome.

Shell plans to drill shallow “top holes” but it won’t go deep enough to reach oil-bearing geological formations. It’s a blow to Shell’s $4.5 billion attempt to be the first company in two decades to drill in the offshore Alaskan Arctic.

The oil company said it would do the preliminary work it could this year “in order to lay a strong foundation for operations in 2013.” Shell announced the decision Monday after an accident during testing of the Arctic Challenger, the troubled oil spill-containment barge.

“During a final test, the containment dome aboard the Arctic Challenger barge was damaged. It is clear that some days will be required to repair and fully assess dome readiness,” the company said in a statement.

The massive containment dome is meant to block releases of oil and natural gas in case of an underwater spill. The company released no details on what happened during the testing in the waters off Washington state.

The Coast Guard, Environmental Protection Agency and the Interior Department said they had no information about what happened to the containment dome. The Interior Department referred questions to Shell.

“The extent and the cause are being investigated now,” Shell spokesman Curtis Smith said.

“We are disappointed that the dome has not yet met our stringent acceptance standards; but, as we have said all along, we will not conduct any operation until we are satisfied that we are fully prepared to do it safely,” Shell said in the statement.

Environmental groups seized on the accident as a sign that Shell shouldn’t be allowed to drill in the Arctic waters. Cindy Shogan of the Alaska Wilderness League said there was no proven method of cleaning up an oil spill in the harsh conditions of the offshore Alaska Arctic and that the incident showed the company wasn’t ready to try. The Natural Resources Defense Council said the “debacle” was just the latest misstep by Shell.

“If you can’t even test your safety systems in calm waters without damaging them, you’ve got no business drilling for oil in the Arctic,” said Niel Lawrence, senior attorney at the environmental group.Environmental groups seized on the accident as a sign that Shell shouldn’t be allowed to drill in the Arctic waters.