The United States briefed NATO (search) allies Monday on plans for an overhaul of American forces in Europe that may see tens of thousands of troops transferred from Cold War (search)-era bases in Germany to new bases closer to potential trouble spots.

The senior State Department and Pentagon officials who met NATO ambassadors declined to give details at a news conference afterward, saying planning remains at an early stage and will only be completed after consultations.

However, U.S. officials have previously said the realignment is likely to close or scale down many of the permanent bases set up in Germany (search) and other NATO nations to face the Soviet threat. Instead troops will be shifted to smaller, lightly equipped centers ready for rapid deployment to places like the Middle East, the Balkans or Central Asia.

"The Cold War's over, we face new threats ... and we need to make sure that our force posture and the posture of NATO and our allies is aligned in such a way to meet these new threats," U.S. Undersecretary of State Marc Grossman said Monday.

After meeting with the 19 NATO allies, Grossman and Undersecretary of Defense Douglas Feith were due to split up for visits to Germany, France, Britain, Turkey, Russia, Poland, Romania, Bulgaria, Italy, Spain and Iceland.

Poland, Romania and Bulgaria have been mentioned as possible hosts of new American bases. Poland joined NATO in 1999. Romania and Bulgaria are set to become full members early next year.

"The recent expansion of NATO ... is an important new reality," Feith said. "Adjustments are going to have to be made to take into account that the alliance is larger than it was a few years ago."

Although Feith said some of the changes could be made next year, the United States is moving cautiously to explain plans to allies where the threat of base closures is politically sensitive. Large U.S. bases often give a significant boost to local economies and provide employment.

Germany is particularly concerned about closures. It is home to the U.S. European Command and hosts about 80,000 of its 116,000 troops.

Many of those troops live in permanent bases set up after World War II that include housing, schooling and entertainment facilities for soldiers' families. The U.S. commander in Europe, Marine Gen. James L. Jones, has called them "small American cities" in Germany.

With the military shifting its focus to more agile forces, such bases will likely be replaced by more semi-permanent ones. Troops would likely rotate in for shorter stints of around six months, but without their families or many of the home comforts found in the old-style bases.

While much speculation of the base realignment has focused on NATO members like Romania and Bulgaria, diplomats at alliance headquarters said the United States could be looking to go still further afield. One option could be making more permanent the U.S. presence at bases in Central Asia that were set up for the war in Afghanistan.

Such a move could upset Russia, which is wary of growing U.S. influence in the region's former Soviet republics. Russian Foreign Minister Igor Ivanov, on a visit to NATO on Thursday, insisted that the U.S. base plans would have to respect existing arms limitation treaties with Russia.

Grossman, who plans to travel to Moscow this week, said the changes would meet treaty commitments.

In other matters Monday, Hungary's Parliament approved a constitutional change allowing the government to deploy troops for NATO operations without securing parliamentary approval. Until now, Hungary was the only member of the alliance that needed to secure parliamentary permission every time its forces were deployed abroad.