U.S. industrial conglomerates, including Ingersoll-Rand PLC and ITT Corp., have become a favorite target of activist investors over the past year. But the head of one such company is trying to stay a step ahead of breakup pressures.

Illinois Tool Works Chief Executive David Speer is ditching a decade-old strategy of building its collection of 800 businesses to more than 1,000. He opened his board to one activist, and recently began selling assets without the public prodding that beset its counterparts.

Today,...