US President Barack Obama acknowledged criticism of his Nobel Peace Prize on Thursday but said he hoped it would subside if he succeeded in his goals, including cutting nuclear weapons and tackling climate change.

Speaking in Norway before collecting the prize, Obama also reaffirmed US troops would begin transferring responsibility for Afghan security to local forces in July 2011 but said there would be no "precipitous drawdown".

Obama will accept the prize just nine days after ordering 30,000 more US troops to Afghanistan to break the momentum of the Taliban.

The escalation of the war effort there, and Obama's failure to achieve breakthroughs on other key priorities such as Middle East peace, have fuelled criticism that the award is premature.

"I have no doubt that there are others that may be more deserving. My task here is to continue on the path that I believe is not only important for America but important for lasting peace in the world," Obama said in response to a journalist's question on how he planned to use the accolade to advance his goals.

He said that meant pursuing a world free of nuclear weapons and countering proliferation; addressing climate change; stabilising countries like Afghanistan; "mobilising an international effort to deal with terrorism that is consistent with our values and ideals"; and addressing development issues.

Some of these initiatives were beginning to bear fruit, Obama told a joint news conference with Norwegian Prime Minister Jens Stoltenberg.

"Force for good"

"The goal is not to win a popularity contest or to win an award ... The goal has been to advance American interests, to strengthen our economy at home and to make ourselves a continuing force for good in the world," he said.

"If I am successful in those tasks, then hopefully some of the criticism will subside, but that is not really my concern.

If I am not successful, than all the praise and awards in the world will not disguise that."     Responding to another question, Obama said July 2011 would signal a shift in the US mission in Afghanistan, when "we are beginning to transfer responsibility to the Afghan people".

But he said the pace of the transfer of authority and "the slope of the drawdown" of troops would depend on conditions.

"It is very important to understand we are not going to see some sharp cliff, some precipitous drawdown," Obama said.

"Now earn it”

Stoltenberg told journalists the prize was well deserved and "can contribute in itself to strengthening the efforts of the president to work for peace".

On a rainy day with temperatures just above freezing, thousands lined heavily guarded Oslo streets to greet Obama, the first US president to visit Norway since Bill Clinton in 1999.

Only handfuls of protesters were visible, with one group holding a sign reading: "Obama you won it, now earn it.”

Environmentalists in the crowd called on the US leader to sign an ambitious deal to fight global warming when he visits nearby Copenhagen next week for the climax of a U.N. climate conference involving nearly 200 countries.

Obama was due to deliver his acceptance speech at 1200 GMT.

He is the third sitting US president, after Theodore Roosevelt and Woodrow Wilson, to win the prize. Jimmy Carter was honoured two decades after he left office. Other prominent Nobel peace laureates include Nelson Mandela, Martin Luther King Jr. and Mother Teresa.

Some polls show that while many Americans are proud Obama is receiving the award, a majority feel it is undeserved. Americans remain anxious about the economy, nudging Obama's approval ratings down to 50 percent or below and potentially hurting his Democratic Party in congressional elections next year.

Many people were stunned, including some in the White House, when the Nobel committee announced in October it was awarding the peace prize to Obama for "his extraordinary efforts to strengthen international diplomacy and cooperation between peoples". – Reuters