UPDATE 1-Major Barnes & Noble investor lowers stake

* Aletheia says it holds 7.67 mln shares, or 12.7 pct

* Says has paid $149.8 million on shares it owns

* Barnes & Noble shares nearly unchanged

NEW YORK, Dec 22 (Reuters) - Barnes & Noble Inc's (BKS.N) third-largest shareholder, money manager Aletheia Research and Management Inc, said it has sold off some of its stake in the largest U.S. bookstore chain.

Aletheia said in a filing with the U.S. Securities and Exchange Commission on Wednesday that as of Dec. 17, it owned 7.67 million Barnes & Noble shares, or a stake of 12.7 percent. That is down from the 14 percent it reported last month. Aletheia owned as much as 15.1 percent earlier this year.

Aletheia began buying Barnes & Noble shares in October 2009. In two months, it amassed 6.8 million shares, raising its stake in parallel with Ron Burkle's Yucaipa Cos, which sharply increased its investment over the same period.

The investors' moves brought accusations by Barnes & Noble that they were working in concert to take over the chain. Last month, Barnes & Noble shareholders ratified an anti-takeover "poison pill" put in place by the board a year earlier.

Barnes & Noble, which put itself for sale last summer, in September beat back an effort by Burkle, supported by Aletheia, to land a seat on the board. But last month, Aletheia voted in favor of ratifying the poison pill.

Barnes & Noble's largest shareholder is Chairman Len Riggio who owns 29.7 percent. Yucaipa owns 18.8 percent of the retailer.

Aletheia said it paid $149.8 million for the 7.67 million shares it holds. Based on a midday stock price of $14.12 on the New York Stock Exchange, those shares are worth $108.3 million.

Barnes & Noble shares were down 0.1 percent. (Reporting by Phil Wahba; Editing by Lisa Von Ahn)