Digital Fortress is about an organization named National Security Agency (NSA) while Deception Point is about National Reconnaissance Office (NRO). Both these organizations are US based and have a significant role in the security of that country.
Digital Fortress revolves around Susan Fletcher- a brilliant, beautiful Cryptographer and an employee at NSA. This book describes how she is able to save the NSA from a conspiracy hatched by the Director of NSA. In this process she gets help from David Becker, a professor at Georgetown University and a brilliant foreign language specialist.
Deception Point revolves around Rachel Sexton-daughter of a politician and an employee at NRO. This book describes how she is able to unmask the NRO director who tries to deceive the whole world by manipulating with the scientific evidence about extraterrestrial life. In this process she gets help from Michael Tolland - an oceanographer and a T.V. presenter.