TRAVERSE CITY, Mich. — A federal agency is delaying an independent analysis of a plan to drop legal protections for wolves across most of the nation because of concerns about the selection of experts to conduct the review, an official said Tuesday.

The U.S. Fish and Wildlife Service in June called for removing gray wolves across the Lower 48 states from the endangered species list, with an exception for the struggling Mexican wolf in the Southwest. Agency director Dan Ashe said the wolf had recovered to the point that it could thrive and even enlarge its territory without federal oversight, although some advocates and members of Congress said the move was premature.

The law requires that a team of scientists evaluate the basis for such a proposal before a final decision is made. The agency hired a private contractor to select and oversee the peer review panel, which is standard procedure to make sure the analysis meets standards for quality and independence, spokesman Gavin Shire said.

The agency isn't supposed to know who the panelists are, Shire said. But the contractor provided a list of candidates that redacted their names but included their professional resumes, which would have enabled the agency to determine their identity, he said.

"What we're doing now is going back and re-examining the process," Shire said. "We've put everything on hold until we've had time to decide how best to proceed."

The move also came after the contractor notified three scientists who were under consideration that their services wouldn't be required. They were among 16 experts who signed a May 21 letter to Interior Secretary Sally Jewell that challenged a draft version of the gray wolf plan. The letter said the wolf has "just begun to recover in some regions and not at all in others."

Shire said he didn't have the names of the three scientists. But the Center for the Biological Diversity, an advocacy group that favors continued federal protection for wolves, identified them as John Vucetich of Michigan Technological University, Robert Wayne of UCLA, and Roland Kays of North Carolina State University.

"Unfortunately, this is but one example of how the Fish and Wildlife Service has been twisting the scientific process to get the desired political result of no more protections for wolves," said Brett Hartl, the center's endangered species policy director.

Vucetich and Wayne told The Associated Press they had received e-mails from the contractor saying they were being excluded from the review team because they had signed the letter. Kays said he had been "solicited as a possible panelist" but later told he wouldn't be needed.

Vucetich, a biologist and wolf specialist, said it was "absolutely wrong" to disqualify an expert from a peer review team because of previous statements about a proposed policy. Any competent scientist will approach such an assignment with an open mind and be willing to alter his or her opinion if new information justifies it, he said.

"As a professional, I've changed my mind on many occasions," Vucetich said. "I make a living out of collecting new data."

Shire declined comment on the dealings with the three scientists, saying the matter was under review. But he said the Fish and Wildlife Service "wanted to be particularly sure that the people we got for this process were objective and unbiased" because the wolf is such a "highly polarizing subject."

The contract with the outside firm has been canceled and the peer review procedure will start over, Shire said. It's unclear whether the delay will affect the timetable for making a final decision on removing wolf protections, which is expected by June 2014, he said.