SFX Broadcasting, New York, said it has entered into a definitive agreement to purchase Liberty Broadcasting, owner-operator of 19 radio stations in six markets. The purchase price is $223,225,000. SFX plans to transfer 11 of these stations to Multi-Market Radio for $100,100,000. SFX Broadcasting will retain stations serving the Washington, Baltimore and Long Island, N.Y., markets. SFX said its business plan is to concentrate on major market stations.