The director of Sen. Edward M. Kennedy's presidential campaign in Virginia said yesterday he expects his candidate to make a good showing at Democratic caucuses around the state on Saturday despite Kennedy's big losses in party contests elsewhere.

Describing his outlook as "upbeat," Ernest Kessler estimated that the Massachusetts senator could chalk up a 20 percent share of the 2,999 delegates who will be elected to the Virginia state convention this weekend.

The kind of outcome, he said, would be all the more dramatic considering that President Carter's chief rival has not won more than 10 to 12 percent of the presidential preference vote in other Southern states.

The Saturday caucuses will choose delegates to both the 10 congressional district caucuses next month and the May 16-17 state convention in Richmond. Sixty-four delegates will be sent to the Democratic National Convention in New York in August.

Kessler conceded that preliminary filling by delegate candidates in caucus contests tomorrow indicated tremendous strength in Virginia for Carter. But he said Kennedy forces have fielded "good size" slates in several urban areas and have been actively courting support in rural districts where delegate candidates do not file before the party meetings.

Nearly all of the pre-filing by delegate candidates has occurred in the urban and suburban areas of the state and does not preclude registered Democrats from attending and participating in the party caucuses held in their jurisdictions. Persons must be in line to register by noon Saturday.

The Kennedy camp, according to Kessler, has intentionally held back on prefiling their candidates in some areas "to give the Carter people less time to react." In Richmond, for example, Kennedy supporters waited until just before the deadline Wednesday evening to pre-file for about 60 percent of the 148 delegate slots. The latest and nearly complete reports on pre-filing show 1,717 delegate candidates for Carter, 601 delegate candidates for Kennedy, 68 uncommitted and a handful of delegate candidates for California Gov. Jerry Brown.

Even as Kennedy backers were optimistic for their prospects tomorrow, the five black members of the Virginia General Assembly -- including the state's only black senator -- were urging Carter's re-election.

"We're dealing here with practical politics," said State Sen. L. Douglas Wilder (D-Richmond) who, speaking for himself and the four blacks who serve in the House of Delegates, stressed that Carter "has not done all those things we had hoped for" on behalf of minorities.

Wilder said Kennedy's bid for support from blacks was not being successful because "his presidential aspirations have fallen on had times."

Supporters of both Carter and Kennedy predicted yesterday that the turnout for Saturday's mass meetings will be low, perhaps under 25,000. Both camps agreed that Kennedy's biggest strength will come from Northern Virginia, with additional significant backing in the Tidewater, Roanoke and Danville areas.