Officials of Internet, the computer network that ties together hundreds of academic, government and corporate networks, are planning to begin a program that will permit users to send messages to one another in what is intended to be an unbreakable code.

At present, users communicating over the network have little privacy. Sophisticated users can easily intercept and read messages.

This lack of security has increasingly worried computer experts as the use of the networks has spread. For many scientists and engineers, the networks have become a mainstay in their communications, used to exchange research results as well as carry on conversations that would otherwise occur over the telephone.

Under the new system, not only can an encrypted message be sent but the message will carry concealed information that will leave no doubt for the recipient that the person who says he sent the message did indeed send it. The recipient will also know with certainty that the message has not been altered. Methods of Assurance