July 31 (Bloomberg) -- Lisa Dennison, director of the Solomon R. Guggenheim Museum in New York, is leaving her post for a top job with Sotheby's as the auction house seeks to strengthen its position in the contemporary-art market.

Dennison, 54, will become executive vice president of the auctioneer's North and South America division in September, said Diana Phillips, Sotheby's worldwide director of corporate affairs, in an interview. Dennison will focus on modern and contemporary art and on ``business development'' and building client relationships, Phillips said.

``We are in an explosive art market, and I wanted to be able to hitch my wagon to their star,'' Dennison said in a telephone interview today. ``I've always thought about a final career and what I might do outside the nonprofit world.''

Dennison declined to discuss how much Sotheby's will pay her and said the company offered her ``considerably more than one makes at a not-for-profit institution.''

In the past, it was taboo for a museum director to take a job in the auction world. Dennison's move reflects the fierce rivalry between publicly owned Sotheby's and Christie's International in the highly competitive market for contemporary art, where the two are riding a 10-year boom in prices. Christie's is owned by the French billionaire Francois Pinault.

``The distinction between the museum world and commerce as two separate estates is not there anymore,'' said Tom Freudenheim, a former assistant secretary for museums at the Smithsonian Institution in Washington who is now retired. ``It shows you how it's all one world and how the museums are cozy with auction houses.''

Poaching in the Past

Sotheby's, the world's No. 2 auction house behind Christie's, has turned to the museum world for talent at least twice before in efforts to close the gap with its rival.

In 1995, Sotheby's hired former Museum of Modern Art director Richard Oldenburg as chairman of Sotheby's America. Charles Moffett was recruited in 1998 to the Impressionist and modern department following six years as director of the Phillips Collection in Washington.

``Lisa has enjoyed broad access to some of the best collectors operating today,'' William Ruprecht, Sotheby's chief executive officer, said in a phone interview today. ``We are making our organization more and more focused on top clients.''

Christie's has beaten Sotheby's for the past five evening, contemporary-art sales periods in New York. The biggest spread occurred in May 2007 when a Christie's sale totaled $384.7 million while Sotheby's brought in $254.9 million.

`Great Asset'

Phillips said Tobias Meyer, Sotheby's worldwide director of contemporary art, had the idea of approaching Dennison about taking the job.

``Tobias had known her for a long time and thought she would be a great asset for Sotheby's,'' Phillips said. Dennison said Meyer approached her in May before the summer art fairs.

``I had been thinking about the business side of art,'' she said. ``Being part of a global network of museums with a strong brand and being part of giving birth to that process has also prepared me for my work at Sotheby's.''

Linked Since 1973

Dennison, who holds a bachelor's degree from Wellesley College and a master's in art history from Brown University, started her career at the Guggenheim as a curatorial intern in 1973 while in college. She joined the Guggenheim full-time in 1978 as an exhibition coordinator. In that job, she worked closely with then-deputy director Diane Waldman.

Dennison was named chief curator and deputy director in 1996. In October 2006, she became the Guggenheim New York's director and was credited with improving the quality and consistency of the museum's curatorial lineup. She was appointed by Thomas Krens, director of the Solomon R. Guggenheim Foundation, which operates museums in New York, Venice, Bilbao, Berlin and Las Vegas.

``What I will miss most about the Guggenheim is the building,'' Dennison said. ``After that, I'll miss the collection because my greatest pleasure at the museum was helping to build it, and after that, I'll miss the people.''

To contact the writers of this story: Lindsay Pollock in New York at lindsaypollock@yahoo.com; Patrick Cole in New York at pcole3@bloomberg.net.

Last Updated: July 31, 2007 16:06 EDT