The Microsoft Corporation announced its first significant software acquisition today, paying $14 million for Forethought Inc. of Sunnyvale, Calif.

Forethought makes a program called Powerpoint that allows users of Apple Macintosh computers to make overhead transparencies or flip charts. Some industry officials think such ''desktop presentations'' have the potential to be as big a market as ''desktop publishing,'' which involves using computers to lay out newsletters and other publications. Microsoft is already the leading software supplier for the Macintosh.

The personal software industry has been buzzing with acquisitions lately. Microsoft has purchased a 10-employee Berkeley company called Dynamical Systems and has invested in another company, Natural Language Inc. But the acquisition of Forethought is the first significant one for Microsoft, which is based in Redmond, Wash. Forethought would remain in

Sunnyvale, giving Microsoft a Silicon Valley presence. The unit will be headed by Robert Gaskins, Forethought's vice president of product development.