Schering-Plough Corp. said it has agreed to sell its Maybelline cosmetics business for about $300 million in cash as part of its plan to concentrate on pharmaceuticals. The buyer is MBP Acquisition Corp., which consists of Playtex Family Products, members of Playtex and Maybelline management, the private investment firm of Thomas H. Lee Co. and certain of the Boston firm's affiliated investment funds, Schering-Plough said Tuesday. Merrill Lynch Capital Markets assisted Schering-Plough in the transaction, which requires government approval. The sale stems from Schering-Plough's decision to concentrate on prescription and over-the-counter drugs as well as personal care and vision care products, said Robert P. Luciano, chairman and chief executive officer of Schering-Plough. In July, Schering-Plough sold its two European cosmetics companies, Rimmel International Ltd. and Chicogo GmbH. Last December, the company announced it was seeking offers for Maybelline. In 1989, Schering-Plough recorded total cosmetics sales of about $300 million, most of which were generated by Maybelline, the company said.