In his last major speech before stepping down as U.S ambassador to the United Nations, Andrew Young last night strongly urged blacks to stay with the Carter administration and to press for full involvement in foreign policy.

Young, in an address to about 4,000 persons at the ninth annual Congressional Black Caucus dinner, also said that Israeli Prime Minister Menachem Begin would be making a serious public relations mistake not to meet with civil rights leader Jesse Jackson, who is scheduled to travel to the Middle East next week.

In a remark that drew a standing ovation, Young said of Begin's announced refusal to meet with Jackson: "Israeli leaders would be making a terrible mistake not to meet with Jesse, for after all they did meet with John Vorster," the former South African white leader.

Young said that Israeli leaders should not fear blacks' increasing interest in international affairs, particularly in the Mideast, because blacks fully understand what Jews have experienced in the Holocaust.

"We've always been for the underdog," he said.

He said that Begin's refusal to meet Jackson would only alienate further those persons who support Israel's right to exist but who also believe that it is necessary to negotiate with the Palestinians to obtain a lasting peace in the Mideast.

Young subtly moved into the section of his speech that called for black support of President Carter. He didn't even mention Carter's name. Instead, he said that he knows that a number of blacks have been waiting for him to "walk away" since he announced his resignation.

"But I am not walking away from anybody or anything" because, he said, he is closely connected with power centers in the federal government. He told the audience, in effect, that it would be foolhardy as well for them to walk away.

"Blacks [presidential appointees] now control $150 billion in this administration," he said. "You might walk away from that, but I am not."

Young also pointed out that blacks have gained a number of federal judicial appointments under this administration and that at least 12 more states still must fill seats in the federal judiciary.

Commenting on the need for black involvement in foreign policy, Young said current international problems have largely been a result of policy being made by "poeple who were never poor . . . who sit in ivory towers talking theory to each other.

"What we need is new input, and that must come from us."