MILWAUKEE — A.O. Smith Corp. announced that it will buy the worldwide motor operations of MagneTek, Inc., for approximately $250 million. The deal, expected to close by the end of this month, would be the largest in A.O. Smith’s 125-year history.

MagneTek makes fractional- and integral-horsepower ac and dc electric motors used in many applications, including commercial air conditioners, air compressors, and spa pumps. Its 1998 sales were approximately $367 million.

The acquisition, combined with its prior acquisitions of the UPPCO subfractional business and General Electric’s compressor motor operation, will take A.O. Smith’s sales to the $1 billion level next year, compared to the sales of $337 million as recently as 1996, said Robert J. O’Toole, company chairman.