The idea of fielding a black Democratic presidential candidate in 1984 made a solid advance at a meeting of national black political leaders here today.

In an all-day session involving about 40 politicians, clergymen and activists, members of the group said support for the idea among the nation's black community has expanded rapidly in recent weeks, partly as a result of the April 12 election victory of Harold Washington, who was inaugurated Friday as Chicago's first black mayor.

In a joint statement, the conferees asserted, "We reaffirm that a black seeking the Democratic nomination for president is a viable option. We affirm the necessity of a candidacy for the presidency which focuses the nation's attention on the urgent needs of our cities . . . ."

"This meeting begins to put in place the mechanism for a national candidacy," said Maryland state Sen. Clarence Mitchell III. "There was no attention to the question of who. We have to make a determination about whether we should go ahead." He said the group will meet again by June 15.

"The only way there would not be a black candidate in 1984 is if no one wants to run--and that isn't the case," said Rep. John Conyers Jr. (D-Mich.).

The Rev. Jesse Jackson, who is scheduled to go to New Hampshire Sunday to canvass for support for a black candidacy, told the group that the idea had moved "from the ridiculous three months ago to the realistic today."

Jackson said tonight that the number of black leaders participating in discussions of a black candidacy has increased, citing the presence today of Mayor Richard Hatcher of Gary, Ind., Del. Walter E. Fauntroy (D-D.C.), Rep. Mickey Leland (D-Tex.) and Coretta Scott King, widow of the civil rights leader.

"We now have a national leadership acting itself into a way of thinking about a presidential candidacy," said Jackson, who is deeply interested in running for the office.

Mitchell said today's meeting had gone a long way to reassure some blacks such as Atlanta Mayor Andrew Young that the effort would remain within the Democratic Party and not result in any black third-party attempt. Young termed the meeting a "very good process."

A major new black voter registration drive is to begin May 15 in the South, where the "Southern Crusade," organized under Jackson's Operation PUSH, has identified about 3 million unregistered black voters.