David W. Fleming has been elected to the board of Valley Federal Savings and Loan Assn., Van Nuys. Fleming, the company's outside general counsel, replaces Donald C. Headlund, former chief executive and president, who resigned from the board. Headlund will remain a Valley Federal employee with consulting responsibilities. Fleming is a senior partner of the Van Nuys law firm of Fleming & Ingalls and has served as the company's general counsel since 1960. His term will expire in April, 1989.