CBS Inc. announced yesterday that it has agreed to buy five radio stations, including Washington's WLTT-FM, from Taft Broadcasting Co.

The transaction, which sources said is worth about $100 million, is subject to federal regulatory approval and the execution of a definitive agreement.

Taft put the five radio stations on the auction block last month, just two months after it had completed its $775 million acquisition of five television stations and seven radio stations from Gulf Broadcast Co. The five radio stations needed to be sold to comply with Federal Communication Commission rules that bar a company from owning both a television and radio station in the same city.

In Washington, Taft already owned WDCA-TV (channel 20) before it obtained WLTT, which calls itself a "light rock" station, from Gulf in February.

As a result of the acquisition, CBS will own seven AM and 11 FM stations. FCC rules permit a single company to own 12 AM and 12 FM stations.

The CBS acquisition comes at a time when the network is in the midst of vigorously fighting a $3 billion takeover bid by Atlanta television magnate Ted Turner.

However, CBS and industry officials said its purchase of the five radio stations were not part of a corporate move to make it more difficult for Turner to win his bid. For one thing, industry officials say, the sale, relatively speaking, is very small compared with the entire CBS operation.

CBS officials add that the company has been interested in adding radio stations to its portfolio for some time, noting that two years ago the company unsuccessfully tried to buy a Dallas radio station.

"We've been on an active search for stations in these markets for some time," said George F. Schweitzer, vice president for communications for CBS Broadcast Group. When Gulf initially put its stations up for sale, CBS made a bid for some of them but lost out to Taft, which agreed to purchase the entire company, Schweitzer said. Then, CBS notified Taft that it would be interested in picking up any of the stations Taft had to spin off as a result of the Gulf acquisition.

"No changes in format are contemplated at all," Schweitzer said. "They are very successful stations in very good markets."