It is up to Congress to decide when the Mall is full. And although in 2003 it declared that no future construction would take place on the land, it can also make exceptions, as it did last week for the new African-American museum, which has been in the works since the early 1900's.

Already, in fact, there are two other projects that have been approved — a visitors' center linked to the Vietnam Veterans Memorial and a memorial to the Rev. Dr. Martin Luther King Jr., to be located near the Jefferson Memorial. And there are several standing proposals for other projects, including a museum dedicated to Latino-American history and a monument to President Dwight D. Eisenhower.

"If Congress keeps making exceptions, then the policy is worthless," said Judy Scott Feldman, president of the National Coalition to Save Our Mall.