Bobb McKittrick, who helped the San Francisco 49ers win five Super Bowls in his two decades as one of the National Football League's premier offensive-line coaches, died yesterday at Stanford (Calif.) University Medical Center. He was 64.

McKittrick had been suffering from cancer of the bile duct. Last spring, doctors canceled a liver transplant after exploratory surgery showed the cancer had spread to the abdomen. McKittrick's on-field coaching duties were assumed by Pat Morris last season, but McKittrick continued to be involved with the 49ers.

Year after year, working with comparatively smaller linemen like Harris Barton, Guy McIntyre and Jesse Sapolu, McKittrick taught blocking techniques that protected Joe Montana and Steve Young, the 49ers' all-pro quarterbacks.

''He has developed more offensive-line knowledge than anyone, ever,'' Bill Walsh, one of McKittrick's head coaches, once said. ''His men have played longer, with better technique, more production, fewer injuries. In every possible category you can measure, he's right at the top.''