BILLINGS — The National Park Service on Tuesday dropped its plan to expand the visitor center at Little Bighorn Battlefield, saying the $1.1 million project would have blemished historic Last Stand Hill.

The expansion had been slated for the base of the hill where Lt. Col. George Armstrong Custer and other members of the U.S. Army 7th Calvary were killed by Sioux Indians in 1876.

Long-term plans for the battlefield, a National Monument, call for a new $11 million visitor center at another location. But since Congress has not provided money for that larger project, park officials had sought to add a new 200-seat theater at the existing center built in the 1950s.

A large group of historians and former park employees pressured the agency to drop the expansion. They filed a lawsuit last month claiming its approval in April had violated environmental and historical regulations.

“Sometimes you just have to admit that you didn’t do your homework as well as you might have thought,” Park Service Regional Director Mike Snyder said in announcing the decision to abandon the project.

Snyder said his agency would come up with another way to accommodate crowds, possibly by altering the existing visitor center without making it bigger.

A Park Service spokeswoman said no timeline or potential cost estimates were available.

Former Park Service Chief Historian Robert Utley, the lead plaintiff in the lawsuit, said Snyder made the right decision.

Utley, 78, worked as a seasonal ranger at the monument in 1952, when the visitor center was dedicated.

“At that time, the National Park Service had a somewhat different philosophy about where to place visitors centers. It was to put them as close as possible to historic resources,” Utley said. “We don’t do that anymore.”

Prior to the lawsuit, filed by Utley and eleven others in partnership with the Washington, D.C.-based Public Employees for Environmental Responsibility (PEER), Snyder already had agreed to review the expansion.

Spokeswoman Karen Breslin said the service had long recognized the visitor center was an “intrusion” on the rolling, grass-covered hills that make up the monument.

“Blemish is the right way to think about it,” she said. “Had the expansion gone forward that would be the issue. It would be a bigger blemish.”

She said the expansion had been proposed out of “frustration” on the part of park employees who deal with large crowds of visitors to the monument every summer.