The White House is considering at least two troop withdrawal options as it weighs a new Iraq strategy: one would carry out President Barack Obama's campaign pledge to get all combat brigades out within 16 months, and a second would stretch it to 23 months, two officials said Friday. A third, in-between option of 19 months also is being weighed, according to the officials, neither of whom would discuss the sensitive topic without being granted anonymity. One of the officials said the main focus appears to be on the 16-month and 23-month options; 23 months would run to the end of 2010. Under either timeline, the United States would hope to leave behind a number of brigades that would be redesigned and reconfigured as multipurpose units to provide training and advising for Iraqi security forces, one official said. These brigades would be considered noncombat outfits and their presence would have to be agreed in advance by the Iraqi government, which under a deal signed late last year insisted that all US forces, not just combat brigades, be out of Iraq by the end of 2011. Obama has said his Iraq policy will include leaving a residual US military force of unspecified composition and size in Iraq and in the region to conduct counterterror missions against al-Qaida in Iraq and to protect American diplomatic and civilian personnel. He has said they will not build permanent bases in Iraq but will continue training and supporting Iraqi security forces "as long as Iraqi leaders move toward political reconciliation and away from sectarianism."