President Barack Obama announced Friday that Gen. James Jones will step down as his national security adviser, the latest in a stream of departures from Obama’s leadership team.

The president will replace Jones with Deputy National Security Adviser Tom Donilon. Jones’ resignation will take effect in two weeks.

During remarks in the Rose Garden, Obama praised Jones for being “a steady voice” throughout their meetings and said he was pivotal in taking on “daunting” challenges, including ending the combat mission in Iraq and sending more troops into Afghanistan. He called Jones a “dedicated public servant and a friend to me.”

The president noted that it was “a difficult decision” for Jones to take the job in the first place because he had recently retired from active duty after more than 40 years of service. Jones ultimately agreed to take the job, but only for two years.

“I am extraordinarily thankful that he agreed to make that additional sacrifice,” Obama said. “Americans owe Jim a debt of gratitude.”

As for Jones’ replacement, the president said Donilon has “a wealth of experience” from having served under three presidents and praised his “probing intellect” and “remarkable work ethic.”

In brief remarks, Jones said he has “enjoyed this assignment enormously” and that he took the job because Obama convinced him that he was “willing to take on the hard issues of our time at a very, very difficult moment in our nation’s history.”

“I find it astonishing [that] in a such a short period of time,” the United States is held in esteem in the rest of the world again, Jones said. “We owe all of this to your leadership, and I thank you for letting me be a part of it,” he told the president.

He added that Donilon is an “extraordinary ally” and “one of the hardest-working human beings I have ever seen.”

Jones’ departure comes as several of Obama’s top advisers have left or signaled they are on the way out. Rahm Emanuel stepped down as chief of staff last week to run for Chicago mayor. Senior adviser David Axelrod plans to leave next year to jump-start Obama’s 2012 presidential campaign in Chicago, and Deputy Chief of Staff Jim Messina is likely to join him. Defense Secretary Robert Gates is also expected to step down sometime after the midterm elections.

Military voices on Capitol Hill had nothing but praise for Jones.

“His service in some of the most challenging and important jobs in uniform, including as commandant of the Marine Corps and Supreme Allied Commander in Europe, rightly earned him distinction. As national security adviser, his demonstrated intelligence and willingness to say what he thinks have served the nation well,” Senate Armed Services Chairman Carl Levin (D-Mich.) said.

“I have been honored to work with General Jones for many years, and I know him as a patriot and strategic visionary whom I trust to always offer his best counsel on national security matters,” House Armed Services Chairman Ike Skelton (D-Mo.) said.

“My sincere thanks go to General Jones for his decades of dedicated service to the United States and I wish him all the best,” he said.