Comcast Corp. today said it had agreed to buy Cablevision Systems Corp.'s stakes in sports networks in California and New England for $570 million in cash, furthering the Philadelphia company's reach into the sports world.

When the deals are completed, Comcast will own 100 percent of FSN New England and 60 percent of FSN Bay Area. The remaining 40 percent will still be owned by an affiliate of News Corp., Cablevision's previous partner.

Cablevision serves about 3 million customers in the New York metrpolitan area.

FSN New England carries Boston Celtics games. FSN Bay Area shows the Oakland A's, San Francisco Giants, Golden State Warriors basketball and San Jose Sharks hockey.

Comcast, which has about 24 million cable customers, already owns eight regional sports networks, including Comcast SportsNet locally, which has the rights to Phillies, Sixers and Flyers games.

"FSN Bay Area and New England are excellent operating businesses and fit strategically into Comcast's portfolio of sports networks," Jeff Shell, President of Comcast Programming Group, said.

Craig Moffett, an analyst with Sanford Bernstein & Co., said the deal makes sense for Comcast. The Philadelphia cable company already is the primary cable provider in both the San Francisco and Boston markets, so the deal gives them additional cross-promotional options, Moffett said.

Although current law requires Comcast to share sports programming in those markets (though not in Philadelphia) with telephone and satellite companies, that could change, possibly making Comcast an even stronger competitor in Boston and San Francisco.