WASHINGTON -- The U.S. board that oversees Radio Free Europe and Radio Liberty has said it will lease their archives for 50 years to a new Prague-based institute being set up by George Soros, the financier and philanthropist.The archives, containing more than 15 million items, are described by scholars as by far the most extensive source of information on the former Soviet Union and its East Bloc partners.Daniel Mica, chairman of the Board for International Broadcasting, the federal funding and oversight agency for the Munich-based radio stations, told a news conference that the new institute will preserve, catalogue and computerize the material after the RFE/RL Research Institute -- which compiled it -- ceases operations by year end.The Soros-founded, New York-based Open Society Institute said it would put up at least $15 million over the next four years to support the new, as-yet unnamed venture.The new institute plans to make the material available eventually to on-line computer users, including via Internet, the network of networks, said Karen Greenberg, executive director of the Open Society Institute.The archives include the largest-known collection of samizdat, or unauthorized writings circulated hand-to-hand in the former East Bloc, as well as some of the most detailed biographical files on Communist leaderships outside U.S. and Soviet intelligence agencies.The RFE/RL Research Institute is being shut to meet congressionally ordered budget cuts at the Munich-based radio service, which is financed by federal grants.The International Broadcasting Act of 1994, signed into law by President Bill Clinton, states that funding of the RFE/RL institute "should be assumed by the private sector at the earliest possible time.""This is the best possible outcome that we could have dreamed of," said Peter Reddaway, a George Washington University political scientist who will be a member of the new institute's seven-person advisory board, along with Soros and Mica.Under the agreement with the Soros group, all archival materials are to be returned at the end of the 50-year custody period.Mica said the new institute would index the archives and make them available to the Library of Congress and former East Bloc nations via CD-ROM, microfiche or whatever the state of the art is at the time