Dell Inc. is trying to sell its computer factories around the world, a move to sharply overhaul a production model that was long a hallmark of the PC giant's strategy but is no longer competitive.

In recent months, according to people familiar with the matter, Dell has approached contract computer manufacturers with offers to sell the plants. One person briefed on the plan said he expects the company to sell most -- and possibly all -- of its factories "within the next 18 months." Other factories could close, this person said....