Carnegie Museum of Art Director Richard Armstrong, who announced in June that he would leave his position by the end of the year, was appointed director of the Guggenheim Museum and the Solomon R. Guggenheim Foundation yesterday.

The foundation's board of trustees unanimously approved Mr. Armstrong' appointment. His last day at the Carnegie will be Nov. 3.

Reached in New York yesterday, Mr. Armstrong said that he was attracted to the Guggenheim position for a number of reasons including "the distinguished staff and a group of dedicated volunteers, a historic collection of great richness, and the iconic architecture, in Bilbao and New York, and, to an extent, Venice."

Add to those qualities "a place that does have aspiration to be global, and that is intriguing."

Louise Lippincott, Carnegie Museum of Art chief curator and curator of fine arts, and Deputy Director Maureen Rolla have been appointed acting co-directors at the Carnegie. They will be jointly responsible for the overall management of the museum while continuing the duties of their respective positions.

Ms. Lippincott has been with the museum for 17 years and Ms. Rolla, nine. They balance the skills of curator and administrator required of a top museum executive.

Mr. Armstrong will be available to provide guidance on a part-time basis through Dec. 4.

Mr. Armstrong, 59, has been the Carnegie Henry J. Heinz II Director since 1996, and will be the fifth director of the Solomon R. Guggenheim Foundation, replacing the flamboyant Thomas Krens who resigned in February.

The Guggenheim directorship occupies a prestigious spot in national and international arts circles. The flagship museum, situated on the tony Upper East Side of Manhattan, is a Frank Lloyd Wright icon with its signature spiral internal ramp of galleries that have been praised in architectural circles while criticized at times as being competitive to the artworks displayed.

Frank Gehry's titanium-plated Guggenheim Museum Bilbao put that Spanish town on the world cultural tourism map when it opened in 1997.

Mr. Armstrong, as director of both the Guggenheim Foundation and Guggenheim Museum, will focus on the role of the New York museum and its collection, a Guggenheim release says. He will also provide management for the other four Guggenheim institutions -- the Peggy Guggenheim Collection in Venice, the Guggenheim Bilbao, the Deutsche Guggenheim in Berlin, and the Guggenheim Abu Dhabi Museum, scheduled to open in 2013.

Last year, attendance at Guggenheim New York was 889,443 and in Bilbao 1,002,963, according to The Art Newspaper.

Combined attendance at the Carnegie Museum of Art and Museum of Natural History in 2007 was 298,252, according to Museum of Art spokesperson Tey Stiteler.

Mr. Armstrong called the Carnegie "an amazing treasure house" and said "one of its strengths is its historical ambition to showcase the world."

"The staff has few parallels, the board is absolutely sterling," Mr. Armstrong said, and he praised the open spaces created by the combination of the original Beaux-Arts building and the addition by architect Edward Larrabee Barnes.

"When you look over the field of available opportunities," he said, "[the Carnegie] is quite at the top."

The New York and Washington, D.C.-based executive search firm Phillips Oppenheim, which conducted the Guggenheim search, has been hired to aid with finding a replacement for Mr. Armstrong.

The search committee, organized by the Carnegie Museum of Art board, comprises Chairman William Hunt; members Lynn Davenport, Milton Fine, Ellen Kessler, Martin G. McGuinn, Lea H. Simonds and Alexander C. Speyer III; and David Hillenbrand, Carnegie Museums of Pittsburgh president and chief executive officer.

Ms. Rolla said yesterday that Mr. Armstrong "leaves us in very good shape." The Carnegie recently completed a strategic plan which provides "a very good plan for this period," Ms. Rolla added.

Ms. Lippincott emphasized that their appointments are temporary, and that they're both hoping "it will be as temporary as possible. The normal length of a search to replace a museum director is about 12 months. Six months would be great."