ANCHORENA PARK, Uruguay — President Bush approved 8,200 more U.S. troops for Iraq and Afghanistan on top of reinforcements already ordered to those two countries, the White House said Saturday, a move that comes amid a fiery debate in Washington over the Iraq war.

The president is sending 4,700 troops to Iraq in addition to the 21,500 he ordered in January, mainly to provide additional support and to handle more Iraqi prisoners than anticipated. He also decided to send a 3,500-member brigade to Afghanistan to accelerate training of local forces, doubling his previous troop increase to fight a resurgent Taliban.

Although officials had foreshadowed the additional forces for Iraq in recent days, the latest troop increase in Afghanistan had not been known and will bring U.S. forces there to an all-time high. The deployments underscore challenges facing the United States in both countries and further stretch a strained military.

In Iraq particularly, the moves could fuel suspicions that a troop increase initially described as a temporary "surge" might grow larger and last longer than predicted.

Bush did not comment on his decision Saturday, the second day of a six-day Latin America tour. But aides released a letter he signed Friday night aboard Air Force One as he flew to Uruguay from Brazil, asking House Speaker Nancy Pelosi, D-Calif., for $3.2 billion in emergency funding to pay for the additional units. The added forces would be split between combat and support units. The proposal would shift $3.2 billion from "lower priority" programs.

The new request also seeks more than $500 million to send additional combat troops, linguists and military trainers to Afghanistan, according to the Office of Management and Budget, "in anticipation of increased combat operations against the resurgent Taliban."

"This revised request would better align resources based on the assessment of military commanders to achieve the goal of establishing Iraq and Afghanistan as democratic and secure nations that are free of terrorism," Bush said in his letter to Pelosi.

The request for additional troops and the spending proposals are likely to figure into deliberations this week over war spending.

Congressional Democrats are struggling to find a way to reverse direction in Iraq. Bush aides have said the president would veto any House Democratic spending plan requiring him to certify the Iraqi government has met certain benchmarks by certain dates to keep U.S. forces in the country. The plan would require, under any circumstance, that troop withdrawals begin March 1, 2008, and that remaining troops be out of combat roles by Aug. 31, 2008.

Pelosi challenged Bush on Saturday over his threat to veto the Iraq spending bill. With a House committee set to consider the approximately $100 billion measure as early as Thursday, Pelosi said a veto would suggest to Iraqi leaders that the United States was not serious about making them more responsible for policing their own country.

"With his veto threat," she said in a statement, "the president offers only an open-ended commitment to a war without end that dangerously ignores the repeated warnings of military leaders, including the commander in Iraq, General Petraeus, who declared in Baghdad this week that the conflict cannot be resolved militarily."

In trying to build backing for the plan, Pelosi and her fellow leaders are drafting a proposal that can satisfy both moderate Democrats worried about a precipitous withdrawal and party members who want to spend money only on a withdrawal. The emerging legislation also will have money for military health care and unrelated provisions that can attract votes.

The New York Times contributed to this report. INSIDE

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