WASHINGTON – Richard Perle, a former assistant secretary of defense, resigned as chairman of a Pentagon advisory group, saying he did not want controversy over a business deal to distract Defense Secretary Donald H. Rumsfeld from the war against Iraq.

“I have seen controversies like that before and I know that this one will inevitably distract from the urgent challenge in which you are now engaged,” Perle wrote in a resignation letter.

Rumsfeld accepted the resignation and said Perle would remain a member of the Defense Policy Board, a bipartisan group that advises him on a wide variety of policy issues. Its 30 members are largely former government officials, retired military officers and former members of Congress.

In a brief statement Thursday, Rumsfeld thanked Perle for his service and said he was grateful the former Reagan administration official had agreed to remain on the board. Rumsfeld made no reference to a reason for Perle giving up the chairmanship.

Perle, 61, has been a vocal advocate of going to war against Iraq and has publicly questioned the reliability of some longtime American allies, including France and Saudi Arabia.

In his letter, made public by the Pentagon and dated March 26, Perle assured Rumsfeld that he had abided by rules applying to members of the Defense Policy Board. He has been chairman of the board since July 2001. The position is unpaid but is subject to government ethics rules that prohibit using public office for private gain.

The controversy centers on Perle’s deal with bankrupt Global Crossing Ltd. to win government approval of its purchase by a joint venture of two Asian firms. Perle would receive $725,000 for his work, including $600,000 if the government approves the deal, according to lawyers and others involved in the bankruptcy case.

The deal is under review by a government group that includes representatives from the Defense Department.

Perle denied any wrongdoing.

“The guiding principle here is that you do not give advice in the Defense Policy Board on any particular matter in which you have an interest,” Perle said in a recent interview. “And I don’t do that. I haven’t done that.”

Perle wrote in his resignation letter that he could not “quickly or easily quell criticism” in the Global Crossing controversy, adding that it was “based on errors of fact.”

Nonetheless, he wrote, “I would not wish to cause even a moment’s distraction from” the war effort.

Perle said he was advising Global Crossing that he would not accept any compensation from the pending sale and that any fee for his past services would be donated to the families of American forces killed or injured in Iraq.

In his written statement, Rumsfeld thanked Perle for his service.

“He has been an excellent chairman and has led the Defense Policy Board during an important time in our history,” Rumsfeld said. “I should add that I have known Richard Perle for many years and know him to be a man of integrity and honor.”