Sept. 12 (Bloomberg) -- Sotheby's has raised its estimate for the auction in London of Russian art collected by the late cellist Mstislav Rostropovich and his wife to as much as 20 million pounds ($40.6 million).

A dozen artworks of the 450 lots being sold on Sept. 18-19 are each worth $1 million or more and the top lot, a painting by Boris Grigoriev, is expected to sell for as much as $4 million, said Sotheby's, the world's second-largest action house.

Sotheby's said the number of items on offer has doubled, with more higher-price art included. In July it gave an estimate of as much as 7.2 million pounds for 200 lots. Rostropovich, who died on April 27 at the age of 80, built the collection with soprano Galina Vishnevskaya, who survives him. The sale is only a portion of their holdings.

An increasing number of wealthy Russians are seeking to acquire works of their cultural heritage. Russia is in its ninth year of economic growth, in large part driven by demand for oil, gas and metals, with the country's new rich spending lavishly on luxury and prestige purchases.

``This is the biggest and best collection of Russian art outside of Russia,'' said Mikhail Kamensky, director of Sotheby's Moscow office. ``This is a great opportunity to acquire art from a unique collection put together by two world cultural figures.''

Items from the czarist period are the most numerous, including late 17th-century enamels, as well as 19th-century porcelain, glass, and paintings. There is also a selection of Russian modernist paintings from the 1920s.

Forced Exile

The collection was assembled over 30 years, starting in the mid 1970s. The couple were forced to leave the Soviet Union in 1974 because the cellist was a critic of human rights abuses. They eventually settled in Paris. Sotheby's said the collection has never been exhibited, published, or loaned.

Prominent Russian buyers have announced they will participate in the sale.

``There are about 10 great lots,'' said Andrei Ruzhnikov, director of Aurora Fine Art Investment, one of whose owners is Russian oil billionaire, Viktor Vekselberg. ``Three paintings by Boris Grigoriev -- lots 423, 424 and 429 -- are the absolute jewels of the sale.''

Grigoriev's ``Faces of Russia,'' (1921) could fetch up to 2 million pounds; ``Portrait of Petr Baksheev in the Role of Vaska Pepel'' (1920) has an estimate of up to 700,000 pounds and ``Self- portrait'' (1938) has a top estimate of 300,000 pounds.

Other highlights include Nikolai Roerich's ``The Treasure of the Angels'' (1905), which might go for 1.2 million pounds. Pieces of porcelain made about 1760 for Count Grigory Orlov could fetch up to 550,000 pounds. Orlov was a lover of Catherine the Great and helped her seize power from her husband, Czar Peter III, in 1762.

Museum Backing

Sotheby's Kamensky said that fewer than 10 state museums in Moscow, St. Petersburg and ``elsewhere in Russia'' are ``interested in bidding.'' Some are hoping to secure government funding, while others have private sponsors, Kamensky said.

While he wouldn't comment which museums might bid, the directors of the State Hermitage Museum, the State Russian Museum, the State Kremlin Museum, and the State Tretyakov Gallery all said they will not bid because of a lack of funds.

The Tsarskoe Selo Museum outside of St. Petersburg is interested in bidding, said Ivan Sautov, the museum's director. Tsarskoe Selo is the only Russian museum known to be active at auctions, and in the past it has bought Russian art at Christie's International, the world's largest auction house.

Sotheby's Russian art sales have risen 20-fold since 2001, and totaled $153.5 million in 2006. So far this year Sotheby's has sold $101 million in Russian art.

To contact the reporter on this story: John Varoli at jvaroli@gmail.com

Last Updated: September 12, 2007 04:41 EDT