WASHINGTON, Jan. 30 — After nearly a century of political infighting and delay, the Smithsonian Institution on Monday selected a prominent space on the Mall near the Washington Monument as the site of its National Museum of African-American History and Culture.

Supporters of the project, including many black cultural, political and academic leaders, who labored for years to have the museum approved, greeted the selection by the Board of Regents, the institution's governing body, with elation.

High-profile advocates of the museum, the institution's first dedicated to a comprehensive study of the black American experience, had told Smithsonian officials that any site off the Mall would be viewed as a slight to African-Americans.

In September 2004 the National Museum of the American Indian opened to much fanfare and high visibility on the eastern edge of the Mall near the Capitol.

Some groups responded to the announcement on Monday with disappointment, arguing that the project would clutter the Mall, the grassy expanse stretching from the Lincoln Memorial to the Capitol.

Smithsonian officials said the vote on the site was not unanimous but would not give details. Officials said they hoped to open the new museum within the next decade.

"My first task for tomorrow is to stop smiling," said Lonnie G. Bunch, director of the museum.

The selection of the five-acre site allows Mr. Bunch to move forward with choosing an architect, as well as to begin raising money and acquiring collections. Cost estimates for the museum, the 19th in the Smithsonian complex, range from $300 million to $500 million. Fifty percent of the cost will be paid by the federal government, the other half by private sources.

The building will probably be at least 350,000 square feet, roughly the same size as the National Museum of the American Indian, Smithsonian officials said.