* Manuscript of Rachmaninoff symphony had been presumed lost
* 320-page document authenticated by British expert
* Score contains details not in other versions, Sotheby's says
By Michael Roddy
LONDON, April 17 (Reuters) - An autograph manuscript score of Sergei Rachmaninoff's Symphony No. 2 that had been presumed lost for half a century will be sold at auction in May, Sotheby's said on Thursday.
The pre-sale estimate for the manuscript of one of the most important compositions in the Russian romantic repertoire is between 1 million and 1.5 million pounds ($1.68-2.52 million), the auction house said in a press release.
"It is one of the few autograph manuscripts of a symphony, central to the international orchestral repertory, remaining in private hands," Sotheby's said, adding that the manuscript contains material absent from any published edition.
The manuscript of the symphony, which had its premiere in 1908 in St Petersburg with the composer conducting, had been on loan to the British Museum for the past 10 years from the Tabor Foundation, which is also a sponsor of the Leeds International Piano Competition.
Sotheby's, in an emailed statement, would not comment on whether the manuscript was being placed for auction by the foundation, saying only it was being sold by "an anonymous consignor". The Tabor Foundation could not be contacted.
The 320-page manuscript had been presumed lost until it was discovered in the estate of a European private collector in 2004, Sotheby's said.
It was listed for auction later that year but was withdrawn from sale "following an ownership claim which has since been settled on terms of confidentiality to the mutual satisfaction of all parties", Sotheby's said.
The authentication of the manuscript, which was missing its title pages, was made by Geoffrey Norris, a leading British expert in Rachmaninoff, Sotheby's said.
Norris, in a 2007 article for The Telegraph newspaper, wrote that when he was asked to authenticate the document in 2004, he travelled by train through the Alps for what he called "a secret assignation at a small railway station by Lake Geneva".
He said that when he examined it, Rachmaninoff's handwriting, manner of making corrections and even the brand of paper led him to conclude it was "unquestionably genuine".
"Aside from the sheer spine-tingling thrill of seeing it, the many alterations, particularly in orchestration, showed how, after finishing his fair copy, Rachmaninoff's thoughts changed in the light of conducting the piece himself," Norris wrote.
The piece has had something of a chequered performance history, with many conductors finding the original hour-long version unwieldy and making cuts that in some versions reduce its playing time to 35 minutes. Most recent performances revert to the un-cut version. ($1 = 0.5955 British Pounds) (Editing by Sonya Hepinstall)