WASHINGTON - A general installed just last month as the Army's top officer is President Obama's surprise choice to become the next chairman of the Joint Chiefs of Staff, two people familiar with the selection process said Wednesday.

Gen. Martin Dempsey, an accomplished veteran of the Iraq war, would succeed Navy Adm. Mike Mullen as the president's top military adviser when Mullen's term as chairman ends Sept. 30. Dempsey would have to be confirmed by the Senate.

Two people familiar with the choice, who spoke on condition of anonymity because the White House has not announced it, said it was scheduled to be made public Tuesday.

Dempsey just began a four-year term as Army chief of staff April 11.

Marine Gen. James Cartwright had long been rumored to be Obama's favorite as the next chairman. But Obama informed Cartwright over the weekend that he was no longer a candidate, a defense official said Wednesday.

It is not unusual for a service chief like Dempsey to be promoted to chairman of the Joint Chiefs, but rarely, if ever, has one been elevated so quickly. Mullen was selected after serving as the Navy's chief for just over two years.

Cartwright, the current vice chairman of the Joint Chiefs, has been a close adviser to the president. Mullen's term began in 2007 under President George W. Bush, and Obama nominated him for a second two-year term in 2009.

Cartwright's chances were hurt by private criticism of his management style and the public release of a Pentagon investigation into claims of misconduct with a young female aide.

The Pentagon's inspector general cleared him of the most serious claims, which suggested an improper relationship. But the investigation found that he mishandled an incident in which the aide was drunk and either passed out or fell asleep in his hotel room, where he was working, as his security personnel stood nearby.

Army Gen. Ray Odierno is said to be a top candidate to replace Dempsey as Army chief. Odierno is commander of U.S. Joint Forces Command, which is being dismantled.

Dempsey is among the most battle-tested of today's four-star generals, with two tours of duty in Iraq and a stint as acting commander of Central Command, which covers most of Central Asia and the Middle East.