First, Peter Duncan, head of Deutsche Shell AG, the German subsidiary, said the company would postpone the sinking to better explain its decision. But within minutes, Mr. Duncan was contradicted by officials from Shell's headquarters in the Netherlands, who said the company planned to go ahead on schedule.

The oil rig is a 300,000-barrel storage platform that previously was use to store oil drilled from the North Sea until it could be shipped by tanker. But in 1991 a pipeline was installed linking the wells with the mainland, making the Brent Spar obsolete.

Shell officials said they had considered pulling the rig to land and dismantling it, as they say they do with all their other rigs. But because the platform had major structural defects in two storage tanks, the prospect of pushing the 460-foot tall steel structure on its side for dismantling posed "very high risk it could break in several pieces," said Bert Regeer, a Shell spokesman in Rotterdam.

Shell argues that the environmental dangers are "almost nil" saying that of the 100 tons of sludge estimated to be in the tanks, 90 percent is sand and 10 percent oil residue akin to what is used to asphalt roads.

"The radioactive material is very small, in the form of salts," Mr. Regeer said. "It is a very small volume, and the radioactive material that is in there is naturally radioactive."

Environmental battles are common in Germany, but oil industry analysts could not remember a time in recent years when the public so quickly and forcefully responded to calls for action.

"The point is that nobody expected such high-level objection to it and this has got to be one of the last things Shell wanted to do in terms of public image," said one oil industry analyst in London. "But now they are towing this thing into the sunset and it doesn't look like they are going to turn around."