Leaders of the NAACP today soundly rejected the idea of a black presidential candidate in 1984, terming it a "hoax" and warning that it could eliminate any black role in selecting the next president.

"I think it's the biggest hoax that's been pulled on black folks that I can think of," Joseph Madison, director of voter registration for the organization, said of such a candidacy at a news conference today.

"The only reason that I believe you are giving this whole black presidential candidacy all the attention that's being given," Madison said, "is because you've got probably six of the dullest, non-charismatic, unattractive white candidates that the Democratic Party has run for president of the United States. At least Rev. Jesse L. Jackson provides color and a kind of rhetoric that folks want to hear."

Earlier this year, the association, the nation's largest civil rights organization, issued a statement that was lukewarm to the idea. The organization was not among the small collection of civil rights groups, church leaders and black politicians who in mid-June endorsed such a candidacy.

That position obviously hardened here at the organization's 74th annual convention.

All six of the announced Democratic presidential candidates have been invited to address the convention, as has Vice President Bush, who is scheduled Friday.

But no forum on the issue, one of the hottest in black political circles, was scheduled in the association's workshops. The principal exponent of a black presidential candidacy, Jackson, of Operation PUSH, who is considering running, was not invited on grounds that he is not an announced candidate.

NAACP executive director Benjamin L. Hooks said that blacks would have to support an electable candidate.

"There's no conceivable chance of a black being elected president of the United States in 1984," Hooks said.

If he were one of the six announced candidates and saw most black voters lining up behind a black candidate, Hooks said, "I would turn my attention to those folk among whom I had a chance, which means that black folks would effectively be ruled out of participating in the platform and the selection of the candidate. We may very well wind up with the more conservative of the candidates."

Yesterday, NAACP legislative director Althea T.L. Simmons released ratings on the civil rights records of the announced Democratic candidates and said a similar report card was being prepared on Reagan.

Asked about Jackson, she said that she did not know how he would rate. She cautioned that it should not be assumed that the NAACP would automatically rate Jackson, a civil rights leader, best on civil rights.

Part of the reason for the lack of unity on a black candidate is that the idea is associated almost entirely with Jackson, who is viewed by many of his civil rights colleagues as self-centered and self-promoting and as an unreliable power broker.

Moreover, many civil rights groups accuse Jackson of trying to co-opt their longstanding voter-registration efforts by announcing his own "southern crusade" to register more than 1 million additional blacks this summer.

Yet many acknowledge that Jackson's appearances in their states as part of that crusade have given their efforts recognition and media attention absent earlier.

The NAACP does not make political endorsements, but its membership includes many of the most reliable black voters. The group is strongest in the South, where the ability of blacks to influence presidential politics is considered greatest.