WASHINGTON - With violence on the decline in Iraq but on the upswing in Afghanistan, President Bush is facing new pressure from the U.S. military to accelerate a troop drawdown in Iraq and bulk up forces in Afghanistan, according to senior U.S. officials.

Administration officials said the White House could start to debate the future of the U.S. military commitment in Iraq and Afghanistan as early as next month.

Some Pentagon officials are urging a faster drawdown of forces in Iraq than envisioned by the White House, which had planned to reduce the number of combat brigades from 20 to 15 by the end of next summer.

At the same time, commanders in Afghanistan are looking for several additional battalions, helicopters and other resources to confront a resurgent Taliban.

Bush's decisions on Iraq and Afghanistan could heavily influence his ability to pass on to his successor stable situations in both countries, an objective his advisers say is one of his paramount goals for his final year in office.

They say Bush will listen closely to his military commanders before making any decisions on troops but is unlikely to do anything he believes could jeopardize recent hard-won security improvements in Iraq.

Administration officials say the White House has become more concerned in recent months about Afghanistan. There, grinding poverty, rampant corruption, poor infrastructure and a growing challenge from the Taliban are hindering U.S. stabilization efforts.

Senior administration officials now say Afghanistan may pose a greater longer-term challenge than Iraq.

"There's a real dilemma there for the U.S.," said retired Lt. Gen. David Barno, a former commander of U.S.-led coalition forces in Afghanistan. "In some ways, the paradox is you could make an argument that the insurgency is diminishing in Iraq and increasing in Afghanistan."

Administration officials said the White House was considering a range of steps to try to stem the erosion, including the appointment of a leading international political figure to try to better coordinate efforts in Afghanistan.

President Bush also plans to step up his personal diplomacy with Afghan President Hamid Karzai and will soon start regular videoconferences with him aimed at more closely monitoring and influencing the situation there, officials said.

Bush has long held videoconferences with Iraqi Prime Minister Nouri al-Maliki.

Afghanistan is so poor and so starved for modern infrastructure, one senior administration official said, that it could well be "a longer, if not larger, challenge than Iraq."

The official, who spoke on condition of anonymity because he was not authorized to speak publicly, said the situation in Afghanistan was "not getting better. It's not getting worse. In a war footing, that's not good enough."

U.S. Army Gen. Dan McNeill, the top NATO commander in Afghanistan, is asking for an additional three battalions of troops from NATO countries - the equivalent of another brigade combat team - but colleagues believe that would not be enough.

U.S. officials are doubtful that allies will provide all the requested troops and predict that Bush will face a request for even more U.S. troops, possibly after attending a NATO summit in April in Bucharest, Romania.

The United States has about 26,000 troops in Afghanistan. NATO provides most of the additional 28,000 foreign troops in the country. Among NATO forces, Britain, the Netherlands, Canada and Australia have assumed the heaviest part of the combat burden alongside U.S. troops.

"I suspect that we will see increasing enemy pressure over time, which may well create demands for combat forces in the future beyond the three battalions cited now," Barno said.

Debate within the administration on Afghanistan and Iraq will come to a head this spring. Gen. David Petraeus, the top U.S. commander in Iraq, is planning to return to Washington with his assessment of whether recent security gains in Iraq can be sustained with fewer U.S. troops, and the NATO summit is expected to focus heavily on Afghanistan.