WASHINGTON - U.S. President Barack Obama vowed on Tuesday to finish the job of an unpopular and costly eight-year war in Afghanistan, and officials said he could announce an increase of around 30,000 troops next week.

Obama said he would soon end weeks of intense speculation about his plans for the way forward in Afghanistan, after a three-month strategic review that has drawn fire from Republican critics who accuse him of dithering.

After eight years, some of those years in which we did not have, I think, either the resources or the strategy to get the job done, it is my intention to finish the job, Obama said at a news conference with Indian Prime Minister Manmohan Singh.

I will be making an announcement to the American people about how we intend to move forward. I will be doing so shortly, he said.

Obama would not be drawn on specifics, but he is expected to unveil his troop decision on December 1, and several U.S. media outlets said it would be in a prime-time television address.

With the U.S. deficit hitting $1.4 trillion, and the White House estimating it will cost $1 million per year for each additional soldier sent to Afghanistan, increasing troop numbers could be a politically risky move for Obama.

He will have to convince Americans, already deeply worried about rising levels of government spending and weary after years of conflict, that Afghanistan is a necessary war or risk punishment in mid-term congressional elections due in 2010.

CHANGES COULD BE MINOR

Afghanistan expert Bruce Riedel, who led the Obama administration's first review of the Afghan war in March, said he did not expect fundamental changes in the U.S. strategy.

This lack of a big shift could be problematic for the president, he said. People may ask why it took three months for him to come up with something that is not very new.

Influential voices in Obama's national security cabinet, including Defense Secretary Robert Gates and military chiefs, favor a U.S. troop increase of 30,000-plus, officials said. The final number could reach 35,000 once U.S. trainers are factored in, but estimates on the number of trainers vary widely.

There are about 110,000 foreign troops, including 68,000 U.S. soldiers, in Afghanistan fighting the Taliban. War spending in Afghanistan has more than doubled over the last year and reached $6.7 billion in June alone.

Obama has been reviewing war strategy since General Stanley McChrystal, the top U.S. commander in Afghanistan, said in a report in September that conditions were deteriorating and 40,000 additional troops were needed to quell the insurgency.

The president stressed that civilian and diplomatic efforts would be key to his strategy and said he would discuss the responsibilities of other nations and Afghanistan itself when laying it out.

One of the things I'm going to be discussing is the obligations of our international partners, he said.

The Afghan people ultimately are going to have to provide for their own security, and so we'll be discussing that process whereby Afghan security forces are properly trained and equipped to do the job, he said.

AMERICANS DIVIDED

Gates, McChrystal, Joint Chiefs of Staff Chairman Admiral Mike Mullen and U.S. Ambassador to Afghanistan Karl Eikenberry will appear before congressional committees in the days after Obama's announcement to testify about the troop buildup.

Obama faces conflicting pressures on Afghanistan.

While military advisers favor a bigger increase, other top White House advisers have been pushing behind the scenes to keep the total number closer to the 20,000-range with a sharper focus on training Afghan security forces, officials said.

Vice President Joe Biden has been a leading skeptic about increasing troops and Eikenberry, who commanded U.S. troops in Afghanistan in 2006 and 2007, has expressed deep concern about sending more troops until government corruption there abates.

Americans are divided on the issue.

Republicans in Congress insist more troops are needed to roll back a Taliban resurgence, while the president's fellow Democrats in general would like to see the United States find a way out of Afghanistan.

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, Obama said.

He signaled that the destruction of al Qaeda and its extremist allies would remain the focus of his new strategy. Some in his administration, including Biden, have questioned the need to send more troops to fight the militant group when it is believed to have fewer than 100 fighters in Afghanistan.

The Pentagon envisages Obama's troop buildup to unfold gradually, with the deployment of approximately one brigade, plus so-called enablers or support troops, per quarter starting by spring 2010, military officials said.

That means the buildup could drag well into 2011, depending on the number and types of brigades sent.

(Additional reporting by Steve Holland, Ross Colvin and Sue Pleming; editing by Eric Beech and Mohammad Zargham)

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