By Phil Stewart

WASHINGTON (Reuters) - The U.S. general nominated to oversee a vast region that includes Afghanistan on Thursday backed keeping Afghan forces at a peak strength of 352,000, contrary to current plans to shrink them after NATO declares the war over next year.

General Lloyd Austin, nominated to lead the U.S. military's Central Command, said at his Senate confirmation hearing that a more robust Afghan force, while more costly, would "hedge against any Taliban mischief" following America's longest war.

"Keeping the larger-size force would certainly reassure the Afghans, it would also reassure our NATO allies that we remain committed," Austin said.

The comments came two days after President Barack Obama announced in his State of the Union address that 34,000 U.S. troops - roughly half of the current U.S. force in Afghanistan - would be withdrawn by early 2014.

Obama reassured Americans that the costly, unpopular war was coming to an end, but he left unanswered bigger questions about America's exit strategy, including how many U.S. troops would stay in the country beyond 2014 to help train and advise the Afghans and to battle remnants of al Qaeda.

Obama also did not discuss the future size of the Afghan forces, although a White House fact sheet sent out after his address noted they would remain at 352,000 until "at least" early 2015.

Austin warned the Taliban would be waiting to test them.

"You could reasonably expect that an enemy that's been that determined, that agile, will very soon after we transition begin to try to test the Afghan security forces," Austin said.

Under current plans, the United States and its NATO allies will help build up the Afghan armed forces to 352,000 personnel, a number they are approaching, but the size of the force - which the allies will continue to fund - will be trimmed to 230,000 after 2015.

ECHOES OF IRAQ

The hearing frequently moved away from questions about the Afghan war and other current events to questions about Austin's past role as commander in Iraq, when a failure to strike an immunity deal for U.S. troops led to their total withdrawal in 2011.

Obama administration officials have warned that failure to strike an immunity deal with Afghanistan would also result in a pullout, but Afghan President Hamid Karzai and U.S. officials have expressed confidence a deal can be reached. Continued...