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.

The MagneTek motor business, with headquarters in St. Louis, operates 12 plants in the U.S., Mexico, the United Kingdom, and Hungary. It employs more than 5,000 people worldwide.