The Senate Armed Services Committee postponed the confirmation hearing of Marine Corps Gen. John R. Allen Jr. to become the commander of allied forces in Europe until after the completion of an investigation into his personal conduct.

Allen, the current commander of all allied forces in Afghanistan, is the subject of a Pentagon inspector general’s investigation regarding a relationship with a woman with links to another imbroglio involving former CIA Director David H. Petraeus. Petraeus resigned last week after an FBI investigation revealed he had an inappropriate sexual affair.

Senate Armed Services Committee Chairman Carl Levin, D-Mich., and the panel’s ranking Republican, John McCain of Arizona announced the delay in a news release.

“Because of the Department of Defense Inspector General’s pending review, the confirmation hearing for General Allen to be Commander of U.S. European Command and NATO’s Supreme Allied Commander has been postponed until a later date,” Levin and McCain said. “That change of command is expected no earlier than March.”

A convoluted string of events has led to the downfall of one of the most celebrated generals in a generation and calls into question another highly regarded military officer.

“This comes as a complete surprise to me,” said Senate Majority Whip Richard J. Durbin, D-Ill. “I need to know more.” Durbin added that the Allen revelations, coming on top of the Petraeus scandal, “raise important questions about leadership in the military.”

Allen allegedly had extensive communications over two years with Jill Kelley, an unpaid social liaison at MacDill Air Force Base in Florida, headquartered at U.S. Central Command. It was Kelley’s concerns about angry anonymous emails she received from Paula Broadwell that led her to ask a friend in the FBI to look into the emails. That FBI inquiry uncovered the sexual affair between Petraeus and Broadwell, who was the general’s biographer. Both Petraeus and Broadwell are married.

Allen succeeded Petraeus as commander of allied forces in Afghanistan in 2011. He is expected to be replaced by Marine Corps Gen. Joseph F. Dunford Jr., the assistant commandant of the Marine Corps. Dunford’s confirmation hearing is scheduled for Thursday and will proceed as planned, according to Levin and McCain. Aides suggested he could be confirmed as commander of allied forces in Afghanistan before the end of this month.

“The uncertainties surrounding the schedule of the new Congress in January make it necessary for the confirmation process for General Dunford to be completed before the end of this year,” Levin and McCain said.

Aides from both the Senate and House Armed Services panels expressed some surprise at the reports, which the Pentagon notified them of Monday night.

Aides also noted that they know very little of the details about the Allen investigation. Defense Secretary Leon E. Panetta has asked the inspector general to look into some 20,000 to 30,000 pages of documents and emails between Allen and Kelley to determine if the relationship was inappropriate, according to news reports. Allen is subject to military law. He has denied any wrongdoing.

A senior House aide said, “This is very troubling. No one wants to rush to prejudge what might be in these emails. It is unclear what Jill Kelley’s role was. There is reason to believe that these events may have been entirely appropriate.”

But the aide noted that such a voluminous amount of correspondence between an unpaid social liaison and the commander of allied forces in Afghanistan did not look good.

Allen oversaw the lion’s share of the president’s surge of about 33,000 troops into Afghanistan, which was drawn down this past summer. He was expected to make recommendations to the president in the coming month regarding the next fighting season, as well as his recommendations for the pace of drawdown leading to most combat forces leaving Afghanistan sometime in 2014. The U.S. military already has begun extensive preparations for the enormous undertaking, and it was widely expected that many lawmakers would press the president for a more accelerated withdrawal. Polls show the Afghanistan War is increasingly unpopular.

Dunford is expected to take over the war strategy by February.