WASHINGTON — Gen. James Jones, the gruff-talking military man President Barack Obama drafted as his national security adviser, announced Friday he was quitting after a tenure marked by ambitious foreign policy changes and undercurrents of corrosive turf battles.

Jones will be replaced by his chief deputy, Tom Donilon, a former Democratic political operative and lobbyist who in many ways is already the day-to-day leader of the White House national security operation. The move deepens a season of White House turnover near the midpoint of Obama’s term, with White House chief of staff Rahm Emanuel departing last week, chief economic adviser Lawrence Summers leaving by year’s end and other changes expected before long.

Obama described the transition from Jones to Donilon as expected and seamless, thanking both men in a sunny Rose Garden ceremony. The president put an emphasis on the patriotism of Jones, a Marine who served in Vietnam and retired as a four-star general after a career of more than 40 years. The two barely knew each other when Jones took the post.

As Obama’s chief national security aide, Jones served during a time when Obama has sought to reshape American foreign policy on many fronts, from ending the combat mission in Iraq to expanding the war in Afghanistan to attempting to improve relations across Europe and Asia.

Jones had quiet clout but found himself in a world of squabbles given the competing demands, ideas and personalities in the government and the challenge of trying to coordinate them through the National Security Council. Questions always seemed to loom over whether Jones’ vast military experience translated as Obama had hoped into the job of national security adviser, which requires informing and counseling the president and coordinating views from agencies.

“Jim has always been a steady voice in Situation Room sessions, daily briefings and with meetings with foreign leaders,” Obama said. He added that Jones had represented the U.S. before its allies in every region of the world, and he said the American people owe the general a debt for making the nation “safer and stronger.”

Jones, 66, is expected to serve in the job for about two more weeks. He recalled that he met Obama just over two years ago and that he was persuaded to join him because of the Obama’s desire to take on the hardest issues of the day in a difficult time for the nation.

The general said, “I believe that where we are today in the global playing field and how the United States is held in the esteem of the rest of the world is an accomplishment that I frankly find astonishing in such a short period of time.” To Obama, he said: “Thank you for letting me be a part of it.”

Donilon’s promotion has a significant spillover effect on the rest of the White House. He had emerged as a top candidate to replace Emanuel as the permanent chief of staff. Now that job appears even more likely to go to Pete Rouse, the newly installed interim chief and a longtime adviser to Obama.

Donilon has played a leading role in the policymaking process that tees up the national security decisions for the president. He has overseen the coordination among deputy chiefs from across the security field and is known for bringing an understanding of domestic policy and politics to the job.

At age 55, Donilon’s route to the national security adviser post has been an unusual one.

He worked as a political aide for Jimmy Carter and Walter Mondale, helped manage Democratic National Conventions, and served in the State Department during Bill Clinton’s presidency. A lawyer, Donilon served for years as executive vice president at Fannie Mae, the mortgage finance company taken over by the government during the economic crisis. He has long been close to Vice President Joe Biden; Donilon’s wife, Cathy, is chief of staff to the vice president’s wife, Jill.

“Over the last two years, there’s not a single critical national security issue that has not crossed Tom’s desk,” Obama said. Expressing a clear comfort level with Donilon, Obama also noted his day-and-night work ethic, drawing laughs when he said it seemed to be fueled by Donilon’s penchant for Diet Coke.

Donilon disclosed last year that he had made at least $3.9 million from his partnership in the O’Melveny & Myers law firm. Donilon’s clients at the firm included Citigroup, Goldman Sachs & Co., Verizon Communications, Obama fundraiser and hotel heiress Penny Pritzker and former EPA Administrator Christine Todd Whitman. Donilon said in his 2009 financial disclosure report that he had sold his individual company stocks.

Jones retained clout and contacts across the military after his Marine career. His White House role was sometimes described in business terms, as a closer who might seal a deal for Obama after others did the legwork. But he had at times a relationship of friction and division with others on the security team.

Jones’ selection as Obama’s national security adviser and his interactions with Obama’s staff were central subjects in Bob Woodward’s new book, “Obama’s Wars.” Woodward, who traveled to Afghanistan for six days in June with Jones, reported that Jones believed Obama’s senior political advisers — including Emanuel, David Axelrod and Robert Gibbs — were obstacles to settling on an Afghanistan policy, failing to attend strategy briefings and at least once blocking his access to Obama. Jones described them in Woodward’s book as “water bugs,” the “Politburo” and the “Mafia.”

As national security adviser, Donilon takes on a deeper role on many of the policy challenges he has already helped shape at the White House — nuclear threats in Iran and North Korea, the threat of terrorism, the wars in the Afghanistan-Pakistan theater. The job comes with enormous demands.

“You have a lot of people outside the building who are rating you on a daily basis, if not an hourly basis,” said James Lindsay, an authority on American foreign policymaking at the Council on Foreign Relations and a former staff member of the National Security Council. “The government is a large and complex operation, and you’re supposed to make it hum, while bringing along Congress, the American public and other countries. It’s a very tall order for anybody.”

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Associated Press writers Anne Gearan, Matthew Lee, Sharon Theimer, Ted Bridis, Pete Yost, Erica Werner and Darlene Superville contributed to this story.

(This version corrects 12th paragraph to reflect that Donilon’s wife is chief of staff to Jill Biden, not Joe Biden.)