Marine Gen. Peter Pace will retire as chairman of the Joint Chiefs of Staff, Defense Secretary Robert Gates announced on Friday.

Gates said while he intended to renominate Pace for another two-year term as chairman, after consulting with congressional leaders, the confirmation hearing was likely to be "a backward-looking and very contentious process."

"The focus of his confirmation process would have been on the past, rather than the future," Gates said at a press conference at the Pentagon.

Instead, Gates he will recommend that President Bush nominate Adm. Mike Mullen, chief of naval operations, as the next chairman of the Joint Chiefs of Staff.

"I think Admiral Mullen will bring a tremendous perspective," Gates said.

• Click here to read Adm. Mike Mullen's bio.

Pace began his term in September 2005 as one of the nation's top two military leaders. Pace serves as principal military adviser to the president, Gates, the National Security Council and the Homeland Security Council. Pace is the first Marine to serve as chairman.

• Click here to read Gen. Peter Pace's bio.

Bush, in Poland after the close of the Group of Eight summit, thanked Pace for his service the past six years.

"President Bush appreciates General Pace's long and distinguished service to the country. He is an example for all our men and women in uniform and has been an integral part of the President's national security team," White House spokeswoman Dana Perino said.

Sen. Carl Levin, D-Mich., heads the Senate committee that will first consider Mullen's nomination. He issued a statement saying the nomination would be the right move, and a renomination of Gates "would have been a backward-looking debate about the last four years."

"I think going in that Admiral Mullen is well-qualified," Levin said.

Levin's Republican counterpart on the committee, Sen. John Warner, of Virginia, also gave a strong vote of confidence for Mullen.

"As we look to the future, in Admiral Mullen, we will have a new hand on the helm, a steady, well-trained hand that will guide and protect the men and women of all of our services, and their familes," Warner said.

Senate Majority Leader Harry Reid issued a statement saying he will focus attention on Mullen's ability to change course in Iraq. He said the same would go for Gen. James Cartwright — currently commander of Strategic Command — who is Gates' choice to be next vice chairman of the Joint Chiefs, succeeding Adm. Ed Giambastini.

"Both men must be advocates for our troops, not for a failed policy. It will require strong leadership to transition the U.S. mission in Iraq so our troops are not policing an Iraqi civil war. They must also refocus on the resurgence of Al Qaeda, rebuild the readiness of the United States military, and fix major problems with the delivery of health care to our troops and veterans," said Reid, of Nevada.

House Armed Services Committee Chairman Ike Skelton, of Missouri, praised the choice of Mullen as the next Joint Chiefs chairman.

"Adm. Mullen is an excellent choice to serve as the next Chairman of the Joint Chiefs of Staff," Skelton said, adding that Mullen "has a solid background of leadership, and I am confident that he will fulfill this role well."

Pace has been either chairman or vice chairman of the Joint Chiefs for the past six years.

Pace, a Vietnam War veteran, will turn 62 in November. He will leave his post when his term ends on Sept. 30, 2007.

FOX News' Bret Baier contributed to this report.