President Obama nominates Marine Gen. Joseph F. Dunford Jr. as the next chairman of the Joint Chiefs of Staff. (AP)

President Obama will nominate Marine Gen. Joseph F. Dunford Jr. to become the next chairman of the Joint Chiefs of Staff, selecting an experienced field commander to guide the United States through familiar insurgent conflicts in Iraq and Afghanistan and new threats from cyberattacks and China’s military rise.

U.S. officials said Obama is expected to announce Tuesday that Dunford, the commandant of the U.S. Marine Corps, is his pick to replace Army Gen. Martin Dempsey, who will step down this fall after four years on the job.

The announcement is the second time that Obama, who has sought to overcome the rocky ties with uniformed leaders that characterized the early years of his administration, has picked a senior officer to provide him with military advice. Dunford must be confirmed by the Senate.

The president will also nominate Air Force General Paul J. Selva, the head of U.S. Transportation Command, as vice chairman, officials said.

Officials said Dunford, a Boston-area native and infantry officer, was a proven combat leader who had distinguished himself as commander of U.S. and NATO troops in Afghanistan in 2013-2014 as foreign forces shifted responsibility for fighting the Taliban to Afghan troops. Dunford also commanded a Marine regiment early in the Iraq war.

“What makes him attractive is that he’s a ground leader, and we’ve still got ground wars going on,” said an administration official, speaking on the condition of anonymity to discuss the selection process.

Retired Gen. James T. Conway, the Marine Corps’ top officer from November 2006 to October 2010, said he had seen Dunford rise to the challenge of big assignments before. While serving under Conway, Dunford was seen as an impressive leader who essentially “skipped a star,” being selected for promotion from one-star general to three-star general in a matter of months. Dunford is the Marine Corps’ second chairman in history, after Gen. Peter Pace, who held the job from 2005-2007.

James Mattis, a retired Marine general who once headed the U.S. Central Command, said Dunford was “unflappable in the face of tension, an excellent listener and superbly accomplished in the operational art.”

Dunford earned the nickname “Fighting Joe” while leading the 5th Marine Regiment as it became the first conventional force to cross into Iraq during the U.S. invasion there in March 2003. His Marines advanced north up Highway 1 from Kuwait, fighting a number of bloody battles while facing problems with weather and limited resources. Twelve Marines were killed and more than 120 were wounded in about a month, according to a Marine Corps unit history.

Once confirmed, Dunford must grapple with a long list of challenges, including deep cuts to military spending, the spread of extremist groups across the Muslim world, and the expansionist ambitions of Russia and China.

Most pressing on Dunford’s first day may be the evolving U.S. operations in Iraq, where about 3,000 U.S. troops are providing advice and training to Iraqi forces battling the Islamic State.

While U.S. and allied airstrikes have helped Iraqi fighters halt the militants’ advance, the group is proving difficult to defeat. As the Iraq conflict unfolds, it will fall to Dunford to advise Obama about whether and how to expand U.S. operations there.

He will also shape decisions about the future of a U.S. mission in Afghanistan. While the remaining U.S. force of 9,800 is supposed to be gone by the time Obama leaves office in 2017, the White House has already shown flexibility in revising earlier troop withdrawal plans. In picking a former Afghanistan commander, well acquainted with the demands of that fight, Obama may be lining himself up for additional pressure to keep troops longer.

Sen. Jack Reed (R.I.), the ranking Democrat on the Senate Armed Services Committee, said Dunford would be well served by his time in Afghanistan, where he commanded foreign troops, guided a complex U.S. operation and contended with the challenges of local politics. “There are few people that have had the experience he’s had,” Reed said in an interview.

The U.S. military has a host of internal problems to solve, including needed reforms to benefits and weapons programs. The new chairman must also help restore the health of a force strained by intense demands and repeated deployments of the post-2001 era.

Dunford will also have to walk a fine line in providing the president advice on military issues with big political ramifications, without veering into politicizing the military. “When that breaks down, it becomes extremely difficult and potentially fraught,” Shawn Brimley, a former White House official now with the Center for a New American Security, said of the need to protect the military’s nonpolitical role.

He will also oversee military ties with a White House that has often been difficult for outsiders to penetrate. As commmander of U.S. forces in Afghanistan, Dunford had more direct interaction with Obama than many generals.

Dunford, known as an intellectual and a soft-spoken leader, did not attend the U.S. Naval Academy like many Marine officers. Instead, he studied at Saint Michael’s, a small Catholic college in Vermont, and later received master’s degrees from Georgetown University and Tufts University’s Fletcher School of Law and Diplomacy.

Dunford will work closely with Defense Secretary Ashton B. Carter, himself only settling into the job after being confirmed in February.

Dunford beat out other military leaders believed to be in the final running for the chairman’s job, including Adm. Samuel Locklear III, expected to step down shortly as head of the U.S. Pacific Command; Gen. Mark Welsh III, the Air Force chief of staff; and Adm. James “Sandy” Winnefeld Jr., Dempsey’s deputy.