Democrats in Northern Virginia's 8th Congressional District yesterday chose five delegates to represent them at the Democratic National Convention this summer -- three committed to President Carter and two supporting Sen. Edward M. Kennedy.

The selection of the delegates from Fairfax and Prince William counties and the city of Alexandria was determined by the results of mass meetings held last month.

The suburban Washington area, generally more liberal than most other sections of the state, gave Kennedy more support than he gathered elsewhere. When the delegate selection process is completed in all the state's congressional districts, Carter is expected to have 59 delegates and Kennedy only five.

Kennedy's supporters have indicated, however, that they plan to stage a credentials fight at the party's state convention in May in a bid to pick up at least one more delegate.

Chosen as Carter delegates to the national convention were George Hampton, a businessman and retired military officer from Prince William County; Nancy Arnesen, a writer and a member of the Alexandria Democratic Committee, and Emily Wyatt, a Fairfax resident who will be going to her first national convention after 30 years of party work. Lester W. Bolton Jr. of Prince William and Donna Poll of Fairfax County were chosen as Carter alternates.

The Kennedys caucus chose Tom Stewart, a congressional aide from Annandale, and Cecily Coleman, a college student from Alexandria as delegates.

Under national party rules, the congressional districts are instructed to divide their convention delegates as equally as possible among men and womenm.