* Obama under pressure to show troop buildup worked
* Violence at its worst across Afghanistan since 2001
* Military and civilian casualties at record highs
By Matt Spetalnick
WASHINGTON, Dec 15 (Reuters) - President Barack Obama, on the eve of releasing a major review of his Afghanistan policy, told lawmakers on Wednesday his war strategy was yielding gradual progress and U.S.-led forces would stick with his approach.
Trying to shore up support from Congress and the U.S. public for his approach in an unpopular war marked by worsening violence, Obama offered what could be a preview of the strategy assessment he will deliver on Thursday.
In a letter to congressional leaders required by law summarizing U.S. military operations overseas, Obama said allied forces were "gradually pushing insurgents to the edges of secured population areas in a number of important regions, largely resulting from the increase in U.S. forces over the past year."
"U.S. and ISAF forces will continue to execute the strategy of clear-shape-hold-build, and transition, until conditions on the ground allow for the full transition of the lead in operations to the Afghan National Security Forces," Obama wrote.
Obama's comments jibed with some conclusions expected in the broader review, which U.S. officials have said will cite areas of progress since the president's decision a year ago to send 30,000 extra troops to reverse the Taliban's momentum and prevent al Qaeda from using the country for safe haven.
Military experts say it is too early to tell whether the strategy will achieve more than the limited military gains seen so far.
But Obama will be under pressure on Thursday to show Americans that the U.S. buildup in Afghanistan is paying dividends and that he will hold to his pledge to begin drawing down forces in July 2011.
WORSENING VIOLENCE
Obama is expected to say on Thursday there have been some advances but that challenges remain and more time is needed to show results.
Violence is at its worst across Afghanistan since 2001, with the insurgency spreading out of traditional strongholds in the south and east into once peaceful areas in the north and west. [ID:nSGE6BE0C4]
Military and civilian casualties are at record highs despite the presence of about 150,000 foreign troops, 100,000 of them Americans.
Obama and other NATO leaders agreed at a summit in Lisbon last month to accept Afghan President Hamid Karzai's timetable for foreign combat operations to end and for Afghan security forces to take over security responsibility from the end of 2014.
Obama's letter also spoke of U.S. anti-terrorism operations against al Qaeda and its affiliates in cooperation with allies around the world, and said his administration remained committed to stepping up such efforts as needed.
"As necessary, in response to the terrorist threat, I will direct additional measures against al-Qaeda, the Taliban and associated forces to protect U.S. citizens and interests," Obama wrote, without naming any countries where U.S. operations might target militants.
The CIA has been conducting an extensive secret campaign using drone aircraft to kill al Qaeda and other militants in Pakistan. There have also been U.S. strikes in Yemen, home to one of al Qaeda's most active affiliates. (Editing by Xavier Briand)
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