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 force levels in Afghanistan, according to senior U.S. officials.

Administration officials said the White House could start to debate the future of the American military commitment in both Iraq and Afghanistan as early as next month. Some Pentagon officials are urging a further drawdown of forces in Iraq beyond that envisioned by the White House, which is set 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 movement.

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 describe as one of the president's paramount goals for his final year in office. They say Bush will listen closely to his military commanders on the ground 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 the situation in Afghanistan, where grinding poverty, rampant corruption, poor infrastructure and the growing challenge from the Taliban are hindering U.S. stabilization efforts. Senior administration officials now believe 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 W. Barno, the 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 is considering a range of steps to stem the erosion, including the appointment of a leading international political figure to try to better coordinate efforts in Afghanistan. European newspapers have focused on Paddy Ashdown, a British politician and envoy, but a former senior military officer said his appointment would be considered controversial and seems unlikely.

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

U.S. Army Gen. Dan K. 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 Bush will be faced with 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-led 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.

U.S. officials said Bush may also consider revamping the current military structure in Afghanistan, which has McNeill serving alongside a four-star NATO commander. Restrictions by NATO members on how their troops can be used -- Germany, for instance, limits where its forces can be deployed -- have made it difficult to mount a coherent response to the Taliban resurgence. U.S. forces, which have been largely confined to a small part of the country in the east, have little presence in the south, where much of the insurgency has taken hold.

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

As the White House looks at Iraq, it once again faces competing pressures from different quarters of the military. At Petraeus's recommendation, Bush has already agreed to withdraw five combat brigades by July, bringing the total down to 15. The Joint Chiefs of Staff want to pull out another five by the end of 2008, on the assumption that 10 brigades would be a sustainable force that would allow them to ease the broader stresses on the armed forces, administration officials say.

Petraeus has been more cautious and may want to keep more troops in Iraq to ensure that security gains are not lost. As violence in Iraq falls, Petraeus's stock has risen sharply within the administration, particularly since his strategy appears to be having an effect, and his views may carry the day with Bush. By contrast, many in the Pentagon opposed this year's troop "surge" and are likely to see their influence with the White House diminished.

"The president will have a lot of different advice between now and March, when General Petraeus and Ambassador [Ryan] Crocker come back from Baghdad and report to the Congress," said White House spokesman Gordon Johndroe. "He's going to listen to what everyone has to say, but at the end of the day, he wants to know what his commanders on the ground say. So he will listen to what General Petraeus says he needs to maintain the security gains we have made in Iraq."

Some who follow Iraq closely say that the current drop in violence is only a temporary result of American and Iraqi money spread to certain tribes, and a calculated gambit by insurgent forces and militias to wait out an anticipated U.S. withdrawal. "Quiet doesn't signify loyalty and quiet doesn't signify surrender," said Michael Rubin, a former political adviser to the initial U.S. occupation authority in Iraq and now a scholar at the American Enterprise Institute. "Quiet signifies that [they] get more from being quiet. . . . What we've gotten is a breather. It's not a permanent truce."

Administration officials and outside experts predicted that Bush will be very cautious about accelerating withdrawals. They note that he was the main instigator of the buildup in Iraq, which added 30,000 troops to the war effort earlier this year, despite heavy pressure from inside and outside the administration to begin withdrawing troops.

A new White House emphasis on Afghanistan would probably expose Bush to even more criticism from Democrats, who have long accused him of taking his eye off the hunt for Osama bin Laden with the invasion of Iraq. "It's about time they recognized the problem" in Afghanistan, said former U.N. ambassador Richard Holbrooke, a Democrat, who says Secretary of State Condoleezza Rice and national security adviser Stephen J. Hadley called him last spring to say that a newspaper column he wrote raising concerns about conditions in Afghanistan was too pessimistic.

But even friends of the White House have voiced concerns. "The strategic consequences of failure in both [Iraq and Afghanistan] are pretty severe," said retired Marine Gen. James L. Jones, former NATO supreme commander, in an interview last month, before his appointment by Rice as a Middle East adviser. "The rest of the world is listening to what we are talking about, and we are not talking about Afghanistan on a daily basis. . . . To the extent that we let that slip out of the headlines, that's a mistake."