Update Monday, May 4: The Associated Press is reporting that President Obama will nominate Marine Gen. Joseph Dunford to be chairman of the Joint Chiefs of Staff, citing White House officials.

WASHINGTON — Gen. Joseph Dunford, the commandant of the Marine Corps, is at the top of the list to become the next Joint Chiefs chairman, according to several sources.

Sources also say the next vice chairman will most likely be Air Force Gen. Paul Selva, head of US Transportation Command.

White House officials have not said when an announcement on the moves will be made, but sources say it should be soon. Whoever is nominated will replace Army Gen. Martin Dempsey.

Other contenders for chairman include Air Force Chief of Staff Gen. Mark Welsh and Adm. Samuel Locklear, head of US Pacific Command, sources said.

However, both men appear to have fallen behind Dunford in the eyes of the White House.

A source Friday indicated on Friday that Welsh is no longer in the running. No reason was given, but Welsh would face a brutal confirmation process if he were nominated. Members of the Senate Armed Services Committee continue to question the service's handling of sexual assault issues, while Chairman Sen. John McCain, R-Ariz., opposes the Air Force's attempt to retire the A-10 close-air support plane.

Locklear, meanwhile, has filed retirement papers with the Pentagon. He is expected to be cleared by the Department of Justice of any connection into the "Fat Leonard" scandal that has ensnared wrapped up a number of Navy officers, which had held up his ability to call it a career.

Dunford, 59, was tapped for commandant of the Marine Corps following a year and a half serving as the commander of the International Security Assistance Force, leading all coalition troops in Afghanistan.

"Fighting Joe" earned his nickname during the 2003 invasion of Iraq, when, as a colonel, he commanded Regimental Combat Team 5 under Gen. James Mattis. A Ranger-qualified infantryman with jump wings and nearly four years spent between Iraq and Afghanistan, Dunford has the physical presence of a warrior: he has a habit of going on seven-mile runs in the heat of the day and completed the Marine Corps Marathon in 2012 with his adult children Patrick and Kathleen at his side.

He's also viewed as one of the Corps' sharpest minds, a graduate of the US Army War College and Marine Corps Amphibious Warfare School with a degree in political science from St. Michael's College in Burlington, Vermont, and dual master's degrees from Georgetown University and the Fletcher School of Law and Diplomacy at Tufts University in Medford, Massachusetts.

But Dunford also has ample experience as a Washington general. He served as assistant commandant under Gen. James Amos from 2010-2012, spearheading programs targeting alcohol abuse among Marines and issuing orders that cracked down on hazing and other "high-risk behavior." He had previously served at the Pentagon as deputy commandant for Plans, Policies and Operations.

During Dunford's Senate confirmation hearing, most questions he fielded had to do with his work in Afghanistan and the future of US operations in the region. He has avoided voicing personal opinions on hot political issues such as ongoing efforts to open ground combat arms and special operations units to female Marines.

In his first six months as commandant, Dunford issued planning guidance that emphasized the Marines' growing relationship with the Navy and its focus on maritime and distributed operations following a decade of land wars in Afghanistan. Dunford also rolled out an ambitious plan to make the Marine Corps force more mature and better trained by adjusting personnel requirements and training for every job and sector in the Marine Corps.

Gen. Paul Selva was appointed head of US Transportation Command in May of 2014. Before that, he spent less than two years as the leader of the Air Force's Air Mobility Command and a year as vice commander with Pacific Air Forces.

Despite a lack of experience in the fighter community that often dominate Air Force leadership, Selva has risen quickly through the ranks, moving from one prestigious command to another. He is well regarded both inside the Pentagon and in industry.

During his three-year stint as assistant to the Chairman of the Joint Chiefs of Staff, he was assigned as a military adviser to the State Department — a notable detail, given that it ties him to then-Secretary of State Hillary Clinton. There has been speculation those ties could lead to Selva being tapped as the next chairman if Clinton wins the White House in 2016.

Although they only overlapped for a few months, Selva and Dunford worked together to facilitate the removal of US equipment from Afghanistan.

Hope Hodge Seck, Andrew Tilghman and Jeff Schogol contributed to this report.