Los Angeles and New York--In a move designed to boost its national presence, radio broadcasting company Clear Communications Inc. said late Monday that it is buying media and broadcasting company Ackerley Group Inc. for $495 million in stock. Under the agreement, San Antonio-based Clear Channel will pay .035 of a share for each Ackerley share, which would value Ackerley at $14.11 a share, a 28% premium above its closing price on Friday. The acquisition should raise Clear Channel's visibility, enabling the company to compete head-on with Viacom Inc.'s Infinity Outdoor business."This transaction allows Clear Channel to enter Boston, Seattle and Portland, Ore., three of the top 25 U.S. outdoor advertising markets," said Clear Channel Chairman-CEO Lowry Mays. Ackerley controls about 90% of those markets.Mays added that the deal would enable Clear Channel to offer more cross-platform advertising opportunities, since it has a radio station, outdoor advertising operation or live entertainment venue in 15 of Ackerley's 18 TV markets.