WASHINGTON: President Barack Obama expects Americans to support sending tens of thousands more US troops to Afghanistan once they understand the perils of losing, and he is preparing to make his case to the American public next week.

Eight years after the September 11 attacks led the US into Afghanistan, Obama said it is still in America’s vital national interest to “dismantle and destroy” al-Qaida terrorists and extremist allies. “I intend to finish the job,” he said. Military officials expect an infusion of approximately 32,000 to 35,000 troops to begin in February or March, the largest expansion since the beginning of the war and one that could bring the cost above $75 billion annually.

Obama said he would announce after Thanksgiving his decision on additional troops, and military, congressional and other sources said the occasion would be last night’s televised speech laying out his plans for expanding the Afghan conflict - and then ultimately ending America’s military role.

Republican critics have been pressing Obama for months to decide on a next step in Afghanistan, but Obama has said repeatedly he was more concerned with making a decision that was right rather than quick.

Neither he nor his advisers has detailed an exit plan, but the strategy he is expected to describe next week would include specific dates that deployments could be slowed or stopped if necessary, a senior military official said. The official and others spoke on condition of anonymity because the decision was not final.

With U.S. combat deaths climbing on Obama’s watch and more than half the American public opposed to escalation, the president seemed to acknowledge yesterday that he has a lot to explain.

“I feel very confident that when the American people hear a clear rationale for what we’re doing there and how we intend to achieve our goals, that they will be supportive,” he said, speaking at a White House news conference with Indian Prime Minister Manmohan Singh.

“I can tell you, as I’ve said before, that it is in our strategic interest, in our national security interest to make sure that al-Qaida and its extremist allies cannot operate effectively” in the area, he said. “We are going to dismantle and degrade their capabilities and ultimately dismantle and destroy their networks.

And Afghanistan’s stability is important to that process.” Returning to a campaign theme, Obama said the Afghan effort had been starved for resources and attention during the Bush administration and he intended to finish the war.

To that end, much of the White House discussion during months of deliberations has centered on how the US would end its military role.

Obama held his 10th war council meeting on Monday evening, and officials said it was his last. Military officials have said Obama is choosing one of the least risky options he was presented, but one still expected to lead to increased US casualties without guarantee of success.

War commander General Stanley McChrystal has warned that the war risks failure without a large troop infusion. Although he preferred a higher figure - about 40,000 - McChrystal is expected to tell Congress next week that this lesser addition still gives him the tools to better combat insurgents in the south and east of Afghanistan. The expected increase would include at least three Army brigades and a single, larger Marine Corps contingent, said officials.