The State Department yesterday abruptly postponed a major conference on Africa that was scheduled to begin next week, apparently under pressure from many of the same black leaders who suggested such a conference last summer.

The black leaders, angered because the department had failed to consult with them to plan the conference and named no black American participants until the late planning stages, sent a telegram from last weekend's gathering of black political leaders in Richmond urging that the conference be postponed or canceled.

A State Department official confirmed last night that the conference had been postponed indefinitely, so that the department could "allow for broader participation." However, the official pointed out that each of the conference's five panels had either a black American or an African member.

Informed sources said Atlanta Mayor Maynard Jackson was the only prominent black invited to participate in the conference's panel discussions, and a spokesman for Jackson said yesterday, before it was known that the conference was canceled, that the mayor had not decided whether to attend.

The spokesman said Jackson had planned to send the State Department a telegram "to encourage key members of the Congressional Black Caucus and particularly another black leader, Mayor Richard Hatcher of Gary, the chairman of TransAfrica," to attend.

Trans-Africa is a Washington-based black-oriented group that lobbies on African issues. Hatcher sent the telegram to the State Department on behalf of the black leaders who met in Richmond.

Jackson's spokesman said the Atlanta mayor was invited to participate in the conference within the last couple of weeks, and sources said the invitation to Jackson came about after some last-minute scrambling by State Department officials in the Bureau of African Affairs.

The State Department official confirmed that Jackson had been invited, but would not give any other names, since the conference was canceled anyway.

Sources listed several other participants, such as former defense secretary and World Bank President Robert McNamara, Rep. Steven Solarz (D-N.Y.) and several Africans teaching at American universities. No other American blacks were mentioned, and the sources said no members of the Congressional Black Caucus were invited.

A congressional foreign relations specialist called the situation "the grossest of oversights," and said it showed the insensitivity in the State Department toward inviting blacks into the foreign policy process. This source called the affair a "bad sign for the administration as a whole."

Sources said the idea for a major conference on Africa was pushed first at the White House and later at State after the Rev. Jesse Jackson, head of the Chicago-based Operation PUSH, returned from a trip to South Africa in early August. Jackson and other black leaders met with President Carter and suggested a meeting to discuss U.S. policies toward southern Africa.

State Department sources said the conference idea came from other sources as well, such as business leaders and other black officials. D.C. Mayor Marion Barry reportedly expressed interest in such a conference to discuss trade with African nations.

A spokesman for Barry said the mayor has been invited to attend the conference, although not as a panel member. Officials noted that there was room for more black participation at the conference after panels divided up onto discussion groups.

Randall Robinson, executive director of TransAfrica, said the black leaders at Richmond were concerned precisely because black Americans were not on the panels and "because we were not involved in the planning."

"We in the black community are committed to put this thing [the conference] on as quickly as possible," but with as much black input as possible, Robinson said.

The State Department official said the administration was not so much embarrassed at the postponement as disappointed.

"We decided it was better to wait on the thing and get everybody involved than to have it be under a cloud," the official said.

The official explained that it would be difficult to reschedule the conference soon, since some poeple would be traveling long distances and many top officials would have difficulty rearranging busy schedules. She also cited other problems, such as the difficulty of reserving conference rooms at the State Department.