A group of black civil rights leaders met with the Palestine Liberation Organization's observer here today and then at a news conference announced their support for Palestinian "self-determination."

The meeting -- more of the continuing chain-reaction from last week's resignation of United Nations Ambassador Andrew Young -- was the most important show of support for the Palestinian cause by any large American group in recent memory.

But while endorsing self-determination, the civil rights leaders -- members of the Southern Christian Leadership Conference, which Young helped found with the late Rev. Martin Luther Kind Jr. -- stopped short of supporting Palestinians' demands for a separate state.

SCLC President Joseph E. Lowery said the black churchmen also spoke to the PLO representative of their belief in non-violence, and urged that the PLO consider recognizing Israel's existence as a state.

The PLO in the past has refused to recognize Israel's right to exist, and has espoused terrorism as a means of reaching its goals.

These urgings did not deter PLO observer Zehdi Labib Terzi, who hailed the meeting as a victory. "We are really happy and gratified that this contact was established. I hope that much more will be learned by the American people," Terzi said.

Young resigned after it became known last week that he had met with Terzi on U.N. business in violation of U.S. policy, which currently forbids substantive contact with the PLO. Blacks have rallied round him since, charging that the Israelis forced his resignation and saying it makes no sense to pretend the PLO does not exist.

The SCLC group plans to meet with Israel's U.N. ambassador, Yehuda Blum, today.

Terzi made yesterday's meeting longer than anticipated, and unexpectedly provided lunch for his visitors in a U.S. private dining room.

Stressing that they support Israeli as well as Palestinian human rights, Lowery and others in the group denied they have become a "constituency" for the Palestinian cause.

"We are not a constituency for either party . . . we hope that our role will be one of building bridges," Lowery said.

Lowery repeatedly ducked reporters' requests for an explanation of what he meant by supporting Palestinians' "right to self-determination in their homeland," and whether this was a call for a separate Palestinian state. One member of the group, however, William Jones, president of the Progressive National Baptist Convention, said that his organization announced its support for a separate Palestinian state eight months ago.

"We know that the interests of Third World people are inextricably related to our own," Jones said.

Another member, Wyatt Tee Walker, indicated there had been some disagreement within the group over non-violence. A minority did not back total non-violence, but recognized the right of "defensive violence" -- kicking back after having been kicked.

Lowery rejected reporters' suggestions that blacks only recently came to support Palestinian rights and that it is inappropriate for the SCLC to concern itself with foreign affairs issues. King involved the organization in opposition to the Vietnam War and called for the United States to restore relations with China, Lowery noted.

Lowery and Walter Fauntroy, the District of Columbia's delegate in Congress and SCLC's chairman, compared yesterday's meeting to early civil rights marches of the sort SCLC sponsored, as a way of focusing attention on issues too long ignored.

"We are the heirs of Martin Luther King," Lowery said at one point.

Lowery also declined to speculate on the possible political repercussions of yesterday's meeting, except to note pointedly that President Carter has no way to stop such sessions. "Since President Carter did not appoint me, he can not disappoint me," Lowery said.

Meanwhile, the Rev. Jesse Jackson, another civil rights activist, said in Washington that black and Jewish leaders wtll meet this week in Chicago in an attempt to mend their strained relations. The meeting has been scheduled for Thursday at the headquarters of Operation PUSH, which Jackson heads.

Jackson described the black-Jewish rift over the PLO issue and Young's resignation as the latest in a series of disputes dating back a decade or more, spanning differences over affirmative action and quotas, Israel's relations with South Africa, and a school-control issue in New York.

But blacks have been drawn prominently into the Israeli-Palestinian debate primarily because they would be most immediately affected by military or economic fallout from another Middle Eastern crisis, Jackson said.

"We're the first to die in a hot war," he said in a conversation with Washington Post reporters and editors, "and we're the first to suffer unemployment in a cold war."

Describing black-Jewish differences as "not to be underestimated . . . but not irreconcilable," Jackson said the two groups have traditionally shared a "concern for decency" but added: "Once we began to move up, the Jews who were willing to share decency were not willing to share power." In particular, he cited opposition by many Jewish leaders to quotas for blacks in education and employment.

Jackson denied that advocacy of a U.S.-PLO dialogue amounted to anti-Semitism, which he described in a speech last weekend as a "white people's mess." Arguing that "racists and anti-Semites are usually one and the same person," he said blacks and Jews have more to gain from uniting than quarreling and called for "black-Jewish dialogues" on all levels, including neighborhoods, churches and synagogues, labor unions and political groups.

Meanwhile, the Congressional Black Caucus postponed a press conference scheduled for yesterday on Young's resignation because, with Congress in recess, only four of the caucus' 17 members showed up.

Staff writer Helen Dewar contributed to this report.