"Black Journal," the longest-running black public affairs program on television, returns for its ninth season at 11 p.m. tonight over WETA-26 with one of the best shows in its uneven history, a first-class discussion of the impact of the black voter turnout last November.

In the 1976 election, 94 per cent of the 6.6 million blacks who voted gave their votes to Jimmy Carter and Walter Mondale, which some have credited with winning the election for the Democrats. To answer the question of what influence this gives the black community, Tony Brown, executive producer and moderator, has assembled a finely honed package of interviews, historical clips of black political activity, footage of Carter campaigning and an independent poll of black leaders.

One of the opinion polls, based on a sample of 100 blacks leaders, asked, "Do you think a Jimmy Carter administration will reward blacks for their support?" Before the Carter Cabinet selections, the response was 80 per cent affirmative. After the cabinet was chosen, with two Cabinet-level black appointess, U.N. Ambassador Andrew Young and Housing and Urban Development Secretary Patricia Roberts Harris, expectations dropped considerably. The same group replied 49 per cent yes.

Other results of the sample indicated the black leaders believe that blacks will continue to vote as a group; the leaders don't think a black will be nominated or elected to the Presidency in 1934; that they believe black voters generally thought they had helped themselves by voting for the Democrats (they also interpreted it as an anti-Ford vote) and that they credit black organizations over labor unions as the impetus for the black voter turnout. The poll also indicated that 69 per cent of the sample thought Young should not have accepted the U.N. post.

The power of the black vote is assessed in crisp interviews with Georgia state Rep. Julian Bond, a latecomer to the Carter side; Benjamin D. Brown, a deputy director for the Carter campaign and now deputy chairman of the Democratic National Committee; Ofield Dukes, an organizer of Operation Big Vote, an umbrella group that encouraged black voter participation and Federal Communications Commissioner Benjamin Hooks, a former judge who will assume leadership of the NAACP this summer.

In the closing commentary, Hooks says, "We are not looking for Jimmy Carter or any other white man to deliver black people but for black people to deliver themselves."

This season "Journal" has dropped its chatty entertainment format of last season for a sharply focused magazine format. Asked about the changes, Brown said the entertaiment: format "was a good idea at the time. Now we've moved and changed to fit the demands of this time."

For the second year the show is being underwritten by the Pepsi-Cola Co., and this year's grant of $275,000 helped give the first of the 13 scheduled shows a very polished appearance.