WASHINGTON: War-weary Americans will support more fighting in Afghanistan once they understand the perils of losing, President Barack Obama declared Tuesday, announcing he was ready to spell out war plans virtually sure to include tens of thousands more US troops.

He is expected to make his case to the nation in a speech next Tuesday night, even as the military completes plans to begin sending in reinforcements in the spring.

Eight years after the Sept. 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.

Republican critics have been pressing him 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 US combat deaths climbing on Obama's watch and more than half the American public opposed to escalation, the president seemed to acknowledge Tuesday 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."

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.

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 Monday evening, and officials said it was his last. The Situation Room sessions that began in September were the most visible markers of a strategic and political debate inside the administration about how to address a resurgent Taliban and other insurgents and whether the US was creating its own enemies the longer it remained.

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 Gen. 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.