U.N. Ambassador-designate Andrew Young said yesterday he wants "very much" to accept an invitation to visit Tanzania, and perhaps Nigeria, early next month to confer with the heads of 15 African nations.

Neither he nor the State Department will make a final decision until the end of his Senate confirmation hearings, which begin Tuesday, Young said, but he conceded that the decision "probably" would be yes.

The trip would be a chance to get a "firsthand understanding of the situation in southern Africa," Young said, adding, "I've been invited to go by one of the men in the world I respect most," President Julius K. Nyerere.

Tanzania's ambassador to Washington, Paul Bomano, last week conveyed a personal invitation from Nyerere for Young to attend a week-long celebration in honor of the merging of two political parties into the Revolutionary Party. The two parties predate the creation of Tanzania in 1964.

The celebration begins Feb. 5, and 14 heads of state from neighboring black African nations will attend.

The trip would be the Carter administration's first direct contact with the front-line countries that have a direct interest in the outcome of the struggle for black majority rule in Rhodesia.

Young said that if time permits, he would stop off in Nigeria "for one day" to visit the Second World Black and African Festival of Arts and Culture in Lagos.

"It's a rare occasion that you get a group like that together in one place," he said of the Tanzanian celebration.

"We hope he will accept," said Bomani. "We would fell honored by his presence. This would symbolize feelings of appreciation for his leadership here [iin the United States] and also make a good start for future cooperation."