2009 Deadliest Year for U.S. in Afghanistan More than twice as many U.S. troops killed in Afghanistan as Iraq.

WASHINGTON, Jan. 1, 2010 -- Eight years after the war began, 2009 was the deadliest year for U.S. service members fighting in Afghanistan and the first time American casualties there exceeded the number in Iraq, Pentagon records show.

More than 312 American soldiers died in Afghanistan last year -- nearly twice as many as in 2008. In Iraq, only 150 Americans lost their lives, half as many as the year before.

December 2009 was also the first month since the U.S.-led war in Iraq began in March 2003 without a U.S. combat death. The three U.S. casualties in Iraq last month were the result of non-combat-related incidents.

Military officials and analysts predict the trend will continue into 2010 as the U.S. continues to draw down forces in Iraq and build up troop levels in Afghanistan as part of President Obama's new military strategy there.

Currently 72,000 U.S. troops serve in Afghanistan with 30,000 expected to arrive by late this year to help fight Taliban insurgents and enhance security for Afghan civilians. By the end of 2010, roughly 100,000 U.S. troops will be stationed in the region.

President Obama announced his decision to send more U.S. forces to Afghanistan in a Dec. 1speech at West Point, following a months-long policy review conducted by his military and civilian foreign policy team.

The administration hopes that the additional troops will produce results similar to the 2007 surge in Iraq, which dramatically curbed violence and has been credited with creating conditions for political stability.

"These are the resources that we need to seize the initiative, while building the Afghan capacity that can allow for a responsible transition of our forces out of Afghanistan," Obama said at West Point. "Just as we have done in Iraq, we will execute this transition responsibly, taking into account conditions on the ground."

But officials have warned that, as in Iraq, the number of U.S. casualties in Afghanistan will likely rise in the short term while forces implement the new mission.

U.S. Military Officials Warn of Increased Casualties

Speaking to a group of 700 Marines at Camp Lejeune, N.C., following the president's announcement,Chairman of the Joint Chiefs of Staff Admiral Mike Mullen said he is certain the military will sustain an increase in casualties this year.

"This is what happened in Iraq during the surge, and as tragic as it is, to turn this thing around, it will be a part of this surge as well," Mullen said. "I expect a tough fight in 2010."

Defense Secretary Robert Gates, in an interview with ABC News' Charles Gibson on Dec. 2, also warned Americans to expect more casualties in 2010.

"Every life is precious. We lost 15 soldiers and Marines in November. We lost 44 in October. Casualties will vary as we go into the winter, but come spring, those casualties will grow," Gates said.

But several military experts say the rise in casualties will likely only be temporary as the surge takes effect.

Retired Army General and ABC News military consultant William Nash says, "there will be more targets, but there will also be more security, which will ultimately decrease casualties."

"The key is going to be synergy between military, politics and economics," he said, adding that prospects are not favorable in the short term. "But over a period of one or two years, I think there's a great opportunity to make progress."

ABC News' Luis Martinez and Nick Schifrin contributed to this report.