RAMSTEIN AIR BASE, Germany (AP) – The Pentagon plans to extend its buildup of several thousand combat troops in Afghanistan, initially announced as lasting until late spring, well into next year, a senior U.S. military official said Friday.

The move comes as U.S. and allied commanders anticipate a renewed offensive this spring by the Taliban, and as they seek additional reinforcements from NATO countries. The effort to bolster forces there so far has brought only limited success, with a few nations promising handfuls of additional troops and equipment.

The extension of the U.S. buildup means American troop levels in Afghanistan, which increased this month to about 26,000 – the highest of the war – will remain roughly the same until at least spring 2008. Until now, a level of 22,000 to 23,000 had prevailed through much of last year.

The decision, expected to be announced in Washington as early as next week, entails sending an Army combat brigade to replace the 3rd Brigade of the 10th Mountain Division when it leaves this spring.

Without replacing that brigade, the number of U.S. troops in Afghanistan would have receded to the lower level. That is because the U.S. has had extra troops in the country since earlier this month, when a brigade of the 82nd Airborne Division arrived.

The official, who spoke on condition of anonymity because the decision has not been announced, declined to identify the replacement brigade. There are about 3,500 soldiers in a brigade.

The move comes as the United States is also adding 21,500 troops to its forces in Iraq, which totaled around 130,000 before that buildup started.

While President Bush’s troop increase in Iraq has aroused widespread public and congressional opposition, there has been little dissent over efforts to intensify U.S. operations in Afghanistan. Both conflicts, however, are continuing to put severe strains on a military that is constantly scrambling to find fresh troops and equipment to send to the war zones.

The increase in the U.S. force in Afghanistan comes as NATO’s new top commander, Gen. John Craddock, is seeking 1,500 to 2,000 extra combat troops for the campaign, plus about 800 more from the British.

Decisions about adjusting U.S. troop levels next year will depend in part on whether the United States’ NATO partners send all the combat and support forces they have promised.

About 15,000 of the American troops in Afghanistan are serving in the NATO-led force, which now totals about 36,000. The other 12,000 are special operations forces or are training Afghan troops.

The 3rd Brigade originally was to go home this month, as it turned over command to the brigade of the 82nd Airborne, but the Pentagon announced in January that it instead will be kept in place four extra months.

Until now, it was not clear whether the Pentagon would replace the 3rd Brigade when it went home.

The senior official, who spoke on condition of anonymity because the decision to extend the buildup has not been announced, said the unit that replaces the 3rd Brigade in late spring will remain for a year.

Thus the number of brigades in Afghanistan, which increased from one to two this month with the 82nd Airborne’s arrival, will remain at that level until the spring of 2008 and possibly beyond, he said.