(For more stories on Afghanistan, click [ID:nAFPAK])
* Decision to spare Afghan people risk, costs - commission
* Karzai faces test of his legitimacy, calls for reform
* White House backs result; says troop decision weeks off
* Abdullah emerges in strengthened position (Adds White House comments, background, paragraphs 2, 7-8, 13; Brown comment, background, paragraphs 22-24)
By Golnar Motevalli
KABUL, Nov 2 Afghan President Hamid Karzai was returned to power after election officials cancelled a needless run-off vote on Monday, but was warned he would need to work harder to retain the West's support after a flawed electoral process.
The result means that Washington and its allies -- engaged in a costly war to stabilize the country -- will have to work with a partner whose legitimacy is bound to be questioned. Karzai himself faces the prospect of having to work with a newly strengthened opposition.
The government-appointed Independent Election Commission (IEC) called off the Nov. 7 presidential run-off a day after Karzai's only rival, former foreign minister Abdullah Abdullah, withdrew citing doubts it would be a fair vote, sparking efforts to have the run-off cancelled.
The IEC, which had said on Sunday the vote would proceed, said it changed its mind to spare the Afghan people the expense and security risk of staging a run-off with only one candidate.
IEC chief Azizullah Ludin told a news conference the commission was also concerned a one-candidate race would raise concerns about the legitimacy of the presidency. The first round of voting in August was marred by widespread fraud in favour of Karzai.
"The Independent Election Commission declares the esteemed Hamid Karzai as the president ... because he was the winner of the first round and the only candidate in the second round," Ludin said, ending weeks of political uncertainty.
In Washington, the White House added its stamp of approval to Karzai's leadership, but with a warning. President Barack Obama was calling Karzai on Monday, spokesman Robert Gibbs said.
Gibbs added the United States was happy that the laws of Afghanistan prevailed but added there would be "tough conversations" with Karzai on issues of governance and corruption. Gibbs said a decision by Obama on whether to send more U.S. troops to Afghanistan was still weeks away. [ID:nN02441954]
Abdullah withdrew on Sunday, sparking a frantic round of diplomatic efforts to have the run-off cancelled. He said he was saddened by the challenges Afghanistan still faces.
"This is not what our people deserved," Abdullah told Reuters. "I'll pursue my agenda for reform and change."
But Karzai still has plenty of support, especially in the Pashtun-dominated south and east. In Herat, an important commercial hub near the Iran border, hundreds of people took to the streets, dancing and singing in celebration.
A weakened Afghan government under Karzai would be a blow for Obama as he considers whether to send up to 40,000 more troops to fight a resurgent Taliban. There are currently around 67,000 U.S. troops and 42,000 allied troops in Afghanistan. [ID:nN01398226]
Several Obama administration officials have said one issue being weighed in Obama's deliberations is whether the United States has a credible partner to work with in Kabul.
Western officials and analysts said it was too late to remove fears about Karzai's legitimacy and that the man who has ruled since U.S.-backed Afghan forces toppled the Taliban in 2001 would have to work harder to keep the West's confidence.
"The credibility of the Karzai government is not going to be simply decided by this election, it will now be decided by the actions the president takes over the coming days and weeks," said a Kabul-based Western official who asked not to be named.
"The first test will be the formation of his cabinet. If he is serious about reform we need to see that," he told Reuters.
But others described the outcome as political expediency. The result came at the end of a tumultuous day that included a surprise visit by U.N. Secretary-General Ban Ki-moon.
"Not only are the citizens of NATO countries with forces fighting here supposed to buy into this hastily cobbled together sham, apparently the Afghan people are as well," said Norine MacDonald, president of think tank the International Council on Security and Development.
Ban congratulated Karzai. But he said in a statement that the "new president must move swiftly to form a government that is able to command the support of both the Afghan people and the international community." [ID:nISL503258]
Many in the West see Karzai as a weak leader at the head of a government riddled with corruption. Critics will want to see him come up with a cabinet acceptable to Afghans and to the country's international partners.
British Prime Minister Gordon Brown said he had spoken to Karzai after he was confirmed president and that he needed to do more to fight corruption and strengthen local governance to reduce the influence of drug barons. [ID:nL2429046]
"Afghanistan now needs new and urgent measures for tackling corruption, strengthening local government and reaching out to all parts of Afghan society, and to give the Afghan people a real stake in their future," Brown said in a statement to parliament.
Britain has around 9,000 troops in Afghanistan and has said it is prepared to send another 500 providing Kabul agrees to provide additional Afghan troops to be trained and fight alongside British forces.
Despite Karzai's win, analysts said Abdullah had emerged in a much strengthened position and as the undoubted leader of a previously fractious and divided opposition. Karzai would have no choice but to work with him, they said.
"Karzai has lost his legitimacy; he is a very weak president and he cannot govern without reaching out to Dr Abdullah," said Kabul-based political analyst Haroun Mir.
Karzai's camp ruled out a power-sharing deal but now may have to name some of Abdullah's team to key posts.
Abdullah said he was open to future talks but also said no deals had been struck in return for his withdrawal, seen by diplomats as one way to spare the country more uncertainty that discredits the government and can only aid the insurgency. (Additional reporting by Sayed Salahuddin, Hamid Shalizi and Yara Bayoumy in KABUL, Keith Weir in LONDON, Steve Holland and Caren Bohan in WASHINGTON; Writing by Paul Tait; Editing by Eric Walsh and Frances Kerry)