WASHINGTON — Though mostly upbeat, the Obama administration’s assessment of war progress in Afghanistan suggests tough combat will continue for years and if the president begins to bring U.S. troops home next summer, as promised, the numbers will be small.

The internal review of President Barack Obama’s year-old war strategy unveiled Thursday says that Taliban momentum has been halted in many parts of Afghanistan and that al-Qaida leaders who are thought to be plotting further terrorist attacks on the U.S. from Pakistan sanctuaries have suffered grievous losses.

But the review makes clear that further progress won’t come easily. And it indicates that ultimate success depends heavily on factors beyond Obama’s control, such as Pakistan’s effectiveness in eliminating al-Qaida and Taliban havens on its side of the border.

"We are on track to achieve our goals," Obama declared from the White House in remarks echoing his announcement a year ago that he was escalating the war effort by sending an additional 30,000 U.S. troops to Afghanistan with the central aim of seizing the initiative from the Taliban.

Though the White House’s rhetoric on the war hasn’t changed much in the past 12 months, other factors have. Public opinion in the U.S. and other coalition countries has soured on the war, casualties have increased sharply and, in the view of some international groups, the outlook for peace has dimmed.

The head of the International Committee of the Red Cross’ Afghan operation said Wednesday, for example, "In a growing number in areas of the country, we are entering a new, rather murky period" in which violence threatens the ability of humanitarian groups to do their work.

Obama’s top national security aides insisted, however, that while tough challenges remain, there is progress toward the goal of handing over control to the Afghan government by the end of 2014.

Defense Secretary Robert Gates, who recently returned from Afghanistan, said at the White House that he saw more progress than he had expected. And he suggested that it can be difficult for those who viewing the war from Washington to grasp how it is unfolding on the ground.

"The sense of progress among those closest to the fight is palpable," Gates said.

This year has been the deadliest in the war for U.S. forces. At least 480 American troops have been killed, compared to 317 last year and 155 in 2008.

Unlike the U.S. role in Iraq, a war that Obama opposed and is drawing to a close, the Afghan conflict has become a defining part of his presidency. He sees it as vital to American security and has tripled the number of U.S. forces there since he took office. Yet only a minority of Americans now support the war in Afghanistan, and Obama’s success or failure in delivering credible, effective leadership in that fight will affect his re-election bid.

Obama has stressed that the scale and pace of U.S. troop withdrawals starting in July 2011 depend on conditions on the ground, meaning mostly the level of extremist violence, the degree of improvement in the Afghan army and police and the capacity of the Afghan government to provide basic services.

He has never said exactly how many U.S. troops will come home next year nor set a timetable for getting all 100,000 out of Afghanistan by the end of 2014, when combat operations are to end. Gates made clear that such calculations are yet to be made.

"I think the answer is, we don’t know at this point," Gates said, adding, "But the hope is that as we progress, that those drawdowns will be able to accelerate."

One reason that any U.S. troop withdrawals next summer are likely to be small is that as Afghan forces assume control in selected districts and provinces, the U.S. and NATO troops they replace will be moved to other, less secure areas.

Some allies, such as Canada, have already said they will end their combat mission next year regardless of how the war is going.

Adm. Mike Mullen, chairman of the Joint Chiefs of Staff, toured small U.S. bases in Afghanistan’s provinces of Helmand and Kandahar on Thursday. He said he saw evidence that the U.S. strategy is paying off with better trust among American and Afghan officers and civilians and signs that local government figures are more responsive and accountable.

"There have been improvements, but there is still a long way to go," he told reporters who accompanied him.

The White House assessment asserted that the Taliban’s momentum had been halted in much of Afghanistan, while cautioning that these gains are "fragile and reversible." Gen. David Petraeus, the top U.S. and NATO commander in Afghanistan, made a similar point in remarks to reporters earlier this month, but with an important caveat not seen in Thursday’s report: The Taliban, he said, still has freedom of movement and momentum in some areas.

Obama cast the war as part of a broader effort to defeat al-Qaida, which is not present in Afghanistan in large numbers but has sanctuary in neighboring Pakistan. He stressed both the threat posed by al-Qaida and the progress that has been made in frustrating the group’s efforts to pursue catastrophic attacks on the United States.

"It will take time to ultimately defeat al-Qaida," he said, "and it remains a ruthless and resilient enemy bent on attacking our country. But make no mistake. We are going to remain relentless in disrupting and dismantling that terrorist organization."

Bruce Riedel, a senior fellow at the Brookings Institution think tank, said the administration was right to make only modest claims of progress in the war.

"We are far from being on the edge of anything anyone would describe as success" in either Afghanistan or Pakistan, he said in a written analysis of the White House review. "Yet at the same time, we are no longer close to the precipice of defeat and strategic disaster as we were when the president inherited the war in January 2009."

While U.S., NATO and Afghan forces have pushed insurgents from their strongholds in southern Afghanistan this year and are aggressively going after militants in the east, the Taliban have opened new fronts in the west and the north where security has been deteriorating.

The U.S. is likely to continue to press the Pakistanis to rout insurgents in North Waziristan, an area along the Afghan border where senior al-Qaida leaders are believed to be hiding. But U.S. officials have concluded that Pakistan is unwilling to mount a major offensive in North Waziristan, partly because the Pakistani army is already stretched.

The White House report offered no concrete proposals for getting Pakistan to do more, saying simply that denying havens for extremists on the Pakistan side of the border "will require greater cooperation with Pakistan," and adding that this will require effective economic development work in addition to military might.

The U.S. has spent far more in Iraq over a shorter period, but costs in Afghanistan are growing. According to the Congressional Budget Office, the U.S. spent an average of $5.4 billion a month in Afghanistan in the budget year that ended in September, and the total cost since the war began stands at $336 billion

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Associated Press writers Anne Gearan, Pauline Jelinek, Ben Feller and Jim Kuhnhenn contributed to this story.