* Allen had been under investigation since November
* No decision yet on Allen's nomination for top Europe post
* Allen preparing options on future US force in Afghanistan (Adds details, comments, background)
By Phil Stewart
WASHINGTON, Jan 22 (Reuters) - General John Allen, the commander of U.S. and NATO forces in Afghanistan, was cleared by Pentagon investigators of allegations of professional misconduct over email exchanges with a Florida socialite, U.S. officials said on Tuesday.
The decision by the Defense Department's Inspector General helps lift a cloud that has hung over Allen, who is married and has two daughters, ever since he became indirectly ensnared in the scandal that forced David Petraeus to resign as CIA director in November.
It could also resurrect the four-star general's military career - although a U.S. official told Reuters that, as of late Tuesday, no decision had been made on whether to proceed with Allen's nomination to become the top U.S. military commander in Europe.
President Barack Obama put that nomination on hold when the investigation was announced in November, even as he expressed confidence in Allen's ability to serve out the final months of his command in Afghanistan.
"With the investigation having only recently concluded, no decisions have been made on moving the nomination forward," the official said, speaking on condition of anonymity. "But it's entirely possible that it could move forward in the days or weeks ahead."
The Pentagon inquiry centered on emails between Allen and Jill Kelley, a Tampa, Florida, resident who knew Allen when he served as the No. 2 officer at the U.S. military's Tampa-based Central Command from July 2008 to June 2011.
The Kelley-Allen emails surfaced when the FBI investigated Kelley's allegations of receiving anonymous, harassing emails from someone else about Petraeus. Those other emails led the FBI to uncover an extramarital affair between Petraeus and his biographer, Paula Broadwell.
But questions about the nature of the Kelley-Allen emails prompted Defense Secretary Leon Panetta to order a Pentagon investigation, a move that triggered a storm of speculation about their relationship.
Kelley, in a piece written with her husband Scott and published on the Washington Post website, said "the insinuation that Jill was involved in an extramarital affair is as preposterous as it is hurtful to our family." A copy of it can be seen here: http://t.co/dj0f4l0c
The investigation also likely took its toll on Allen. Minimally, it limited his contact with the media as he was wrapping up his time in Afghanistan and preparing options for Obama on the future U.S. military presence once NATO declares the combat mission over at the end of 2014.
The White House is considering options for keeping between 3,000 and 9,000 troops in Afghanistan, officials have said - a lower range than Allen had initially recommended.
Panetta was described by his spokesman to be "pleased to learn that allegations of professional misconduct were not substantiated by the investigation."
"The Secretary has complete confidence in the continued leadership of General Allen," spokesman George Little added.
If his nomination does proceed, Allen could still potentially face questions about the email exchanges at a Senate confirmation hearing for the job as head of U.S. European Command and Supreme Allied Commander Europe. (Editing by Sandra Maler, Stacey Joyce and Lisa Shumaker)