WASHINGTON (AP) _ Three South African black leaders said Tuesday that their country's black population would suffer economically if congressional proposals to reduce U.S. trade and financial ties with South Africa are enacted.

''I am entirely against apartheid, but disinvestment is not the solution,'' said Silumi Arthur Mpondo, an elected member of the town council of Ibhayi.

Mpondo is part of a delegation that has come to the United States to rally opposition to a proposal introduced by Sens. Edward M. Kennedy, D-Mass., and Lowell Weicker, R-Conn., which would bar new U.S. investment in South Africa, computer sales to that country and the importation of South African gold coins.

The week-long visit by the delegation is being sponsored by a private South African anti-Marxist group called Victims Against Terrorism.

Mayor Tamsanqa Linda, who represents 400,000 people in Eastern Province, said the legislation would be ''suicide'' for South Africa's blacks.

''The people who are calling for disinvestment have no following,'' he told the news conference.

Pastor Ndabezinhle Bongani Musa, an ex-Marxist, criticized the U.S. press for the attention which he said it has lavished on Bishop Desmond Tutu, the anti-apartheid Nobel Peace Prize winner.

He said Tutu ''has never stood up to say the violence in South Africa must stop.''

The news conference was convened by the Rev. Jerry Falwell, president of the Moral Majority, and Howard Phillips, chairman of the Conservative Caucus. Both assailed the U.S. media's ''one-dimensional reporting'' of recent developments in South Africa.

Phillips, who recently returned from a 10-day South African visit, said the ''American people are being denied important facts concerning the sources of violence and unrest in South Africa.

''Destabilization of South Africa is a No. 1 short-term geostrategic objective of the Soviet Union and her Marxist-Leninist operatives worldwide,'' he contended. ''Their goal is revolution, not reform.''