Forgea, a mixed-breed terrier, has become the focus of international attention and a $50,000 rescue effort by the Hawaiian Humane Society and the U.S. Coast Guard.

But the growing threat that the tanker and its cargo of 60,000 gallons of diesel fuel and lube oil washing up on a reef prompted the Coast Guard to send a tugboat to stop it, said Lt. DesaRae Atnip, a Coast Guard spokeswoman in Honolulu.

The tugboat could reach the tanker as early as Friday.

Sailors from a pair of Honolulu-based long-line fishing vessels which found Insiko on Sunday, tried unsuccessfully to convince Forgea to leave the tanker. They gave up on Tuesday.

The tugboat crew has orders to try to rescue Forgea and retrieve the body of an Insiko crewman killed when the tanker caught fire, Atnip said. The tanker's other 11 crewmen were rescued April 2, but for unexplained reasons, Forgea was left behind.

No decision has been made, but the tanker will likely be scuttled at sea.

"We are still evaluating everything, but we are certainly leaning toward sinking the vessel," Atnip said. "They are going to do everything they can to get that dog off there - up to the point of endangering lives."

If the ship runs aground on Johnston Atoll, pristine reefs, thousands of sea birds, hundreds of endangered green sea turtles and a handful of endangered Hawaiian monk seals could be harmed, said John Naughton, Pacific islands environmental coordinator for the National Marine Fisheries Service.

"There is a good potential she will run aground on the eastern reef of the atoll and we could have a real ecological disaster, not only from the grounded vessel, but from the 60,000 gallons of fuel and oil," Naughton said.

He said his agency hoped that as much of the fuel and oil as possible would be removed from the ship and then it would be scuttled southwest of Johnston Atoll.

"Most of the fuel will go down with the vessel and remain locked inside," Naughton said.

Naughton said letting it continue to drift at sea was unacceptable. "Sooner or later it will only end up on someone else's reef," Naughton said.

Meanwhile, Coast Guard officials in Honolulu fended off a barrage of angry phone calls and e-mail from members of the Humane Society of the United States, Atnip said. The animal group had told its 14,000 members Wednesday in an e-mail alert that the Coast Guard planned to sink the Insiko with Forgea aboard.