The Obama administration has decided to remove two of the four U.S. Army brigades remaining in Europe as part of a broader effort to cut $487 billion from the Pentagon’s budget over the next decade, said senior U.S. officials.

The reductions in Army forces, which have not been formally announced, are likely to concern European officials, who worry that the smaller American presence reflects a waning of interest in the decades-long U.S.-NATO partnership in Europe.

Top Pentagon officials have sought to allay the concerns by telling their NATO allies in private meetings that the United States will continue to rotate Army units through Europe on training missions to augment the presence of the remaining two brigades.

“In the briefing we’ve been giving the Europeans, we have made clear that there is going to be this rotational presence there that will be conducting exercises,” Defense Secretary Leon E. Panetta said in an interview.

“As a matter of fact, they will probably see more of the Americans under the new strategy because the brigades that were there were actually fighting in Afghanistan and weren’t even there. . . . What you are going to have is two [brigades] plus this large rotational presence that is going to be there.”

The reductions are part of a Pentagon plan to shrink the Army from its current 560,000 soldiers to about 490,000, defense officials said. The cuts are being driven by a new defense strategy that calls for smaller, faster and more agile forces and a shift in focus toward the Asia-Pacific region, where China has been investing in submarines, fighter jets and precision-guided missiles.

Senior Obama administration officials have targeted Europe for cuts because they recognize that reductions in U.S. forces abroad will generate less congressional outcry than cuts in the United States, where the soldiers pump money into local economies.

The U.S. military maintains about 80,000 troops in Europe from all of the services. Cutting two Army brigades and the noncombat units that support them will result in a reduction of about 10,000 to 15,000 soldiers.

Panetta’s idea of augmenting American presence around the world by rotating combat brigades or smaller Army units through areas on training exercises is a relatively new concept for the regular Army, which has historically maintained a more static, garrison-based force in Europe.

During the past decade, the Army’s combat brigades have rotated with little rest to Iraq and Afghanistan on 12- to 15-month tours.

“If we can develop these innovative rotational presences elsewhere, we will be in a position to basically cover not only the areas where we are keeping a key focus — the Pacific and the Middle East — but we will be covering the world,” Panetta said.

He said the Pentagon envisions sending Army units to areas such as Latin America and Africa on training exercises as the Obama administration continues to cut the size of the U.S. force in Afghanistan. Such missions have typically been conducted by Army Special Forces units and the Marine Corps.