The most-visited museum in the world has a new boss: Gen. John R. Dailey has been named director of the Smithsonian's National Air and Space Museum.

Dailey, 65, currently NASA's associate deputy administrator, will take over at the museum in January. He succeeds Donald Engen, who was killed in a glider accident in July.

Working at his NASA office yesterday when his appointment was announced, Dailey declined to comment on his new job. But the Smithsonian issued a press release quoting him: "It is an honor to have been selected as the director of the National Air and Space Museum. Admiral Don Engen was a very close friend, and I consider it a privilege of the highest order to be able to carry on his vision."

Before coming to NASA in 1992, Dailey spent 36 years in the Marine Corps, flying 450 combat missions in Vietnam and retiring as assistant commandant. He was awarded the Distinguished Flying Cross, the Bronze Star and the Combat Action Ribbon, among other decorations.

"He is a most impressive individual," said Smithsonian Secretary I. Michael Heyman in a press release. "He will continue the strong, dedicated leadership that we have come to expect at Air and Space."

Heyman won't get a chance to work with the man he praised yesterday: He is retiring in January and will be replaced by Lawrence M. Small, 59, a former banker and head of Fannie Mae.

Air and Space, which opened in 1976, is the busiest of the Smithsonian museums, attracting nearly 10 million visitors a year to its facility on the Mall, which houses the Wright Brothers Flyer, the Spirit of St. Louis and thousands of other aviation artifacts.

Dailey will find himself in charge of 260 employees and a budget of about $25 million. He will also oversee the construction of the museum's new facility, a 710,000-square-foot hangar-style building scheduled to open at Dulles International Airport in December 2003. It will display more than 180 aircraft and 100 spacecraft, far more than can be exhibited in the museum's Washington facility, which will remain open after the Dulles Center is completed.