A computer programmer who was dismissed from his job at a New Jersey engineering company has been charged with planting a computer ''bomb'' that deleted software critical to the company's operations and caused the loss of more than $10 million in sales and contracts, according to court papers unsealed yesterday.

Federal prosecutors believe that the programmer, Timothy A. Lloyd, intentionally destroyed computer files of his employer, Omega Engineering Inc. of Bridgeport, N.J., because he was upset over the loss of his job. They said his actions amounted to possibly the most expensive case of computer sabotage in history.

Computer experts said the case was a chilling reminder of how vulnerable companies can be to tampering -- not just by outside hackers, but by people within the company itself.

''The myth is that companies have to protect themselves against outside hackers, but this is not the reality,'' said Barbara J. Bashein, professor of information systems at California State University at San Marcos. ''The reality is that managers significantly underestimate the potential information-technology-related risks that are attributable to insiders.''