President Barack Obama’s longest-serving foreign policy aide, Mark Lippert, is leaving the White House to serve as an intelligence officer in the U.S. Navy.

Lippert, a 36-year-old Navy reservist and Iraq war veteran, will leave his job as chief of staff for the White House National Security Council to return to active duty, a White House statement said.

The White House did not say where Lippert would be deployed.

Lippert’s departure was described in some media accounts as a “shakeup” but White House sources said he would be back after his service is up in six to nine months.

Obama, himself, said Lippert would be welcome back at the White House anytime.

Lippert joined Obama’s Senate staff in 2005 and later was a top foreign policy aide on Obama’s presidential campaign, but left for nearly a year when he was called up to advise the Navy SEALs on intelligence in Iraq. Lippert returned from Iraq in mid-2008 and became a regular presence on Obama’s campaign plane during the final stretch against Republican John McCain.

Obama called Lippert a “close friend” and said he would miss “his counsel, his excellent work at the NSC, and his good cheer.”

“At the same time,” Obama added, “I was not surprised when he came and told me he had stepped forward for another mobilization, as Mark is passionate about the Navy. I support his decision.”

Obama said that Lippert would “always have a senior foreign policy position in this White House, when he chooses to return to civilian life.”

Denis McDonough, who worked closely with Lippert on the campaign and at the White House, will succeed him as chief of staff to the National Security Council.

Ben Rhodes, another longtime Obama aide who has been serving as the top foreign policy speechwriter in the White House, will take over from McDonough as the point person at the NSC in charge of strategic communications.

Photo Credit: Reuters/Jim Young (Obama speaks to troops in Iraq in April)