JOHANNESBURG, AUG. 14 -- South Africa took another step toward breaking out of its diplomatic isolation today as President Frederik W. de Klerk paid a one-day state visit to Madagascar, a former French colony that had long shunned the white-ruled Pretoria regime because of its policy of racial separation.

Reports from Antananarivo, capital of the large island state off the east coast of Africa, said De Klerk had signed an economic and commercial cooperation agreement with Madagascan President Didier Ratsiraka.

Madagascar also granted landing rights to South African Airways, which is excluded from most other African countries, the reports said. Under terms of the agreement, there will be weekly flights from South Africa to Madagascar beginning Sept. 1, but Ratsiraka refused to grant the airline overflight rights, meaning that its planes will have to continue navigating around the island on routes to the Far East.

The invitation to de Klerk from Madagascar came as a suprise to Western diplomats here because Ratsiraka, a backer of Nelson Mandela's African National Congress, is a strong critic of South Africa's white-minority government and a supporter of sanctions against it.

The first sign that De Klerk's reformist policies were leading to a reassessment of attitude toward Pretoria by black African leaders came when De Klerk attended the Namibian independence celebrations last March -- a few weeks after he lifted the ban on the ANC and released Mandela, its celebrated leader.

In two days of subsequent meetings in Namibia, the leaders of more than 17 countries, nearly half of them African, met with De Klerk prompting him to predict that "South Africa's diplomatic relations will broaden within the next few months and years."

That has not happened yet, but there have been further signs of a thaw in attitudes and a growing interest in establishing trade relations with South Africa, which has the continent's most highly developed economy.

In Madagascar, socialist policies insituted by Ratsiraka in the 1970s made the country one of the poorest in the world and caused him to switch to a free-market system in the late 1980s. As he has sought ways to revive the economy, Ratsiraka appears to be looking with new interest at South Africa as a trading partner, but he declared as recently as four months ago that he could not restore economic ties with Pretoria until it outlaws racial repression.

In South Africa today, violence continued between blacks and white extremists, and fighting spread between rival supporters of Zulu Chief Mangosuthu Buthelezi's Inkatha movement and the ANC.

Fifteen people were killed last night and about 200 injured in fighting between migrant Zulus loyal to Inkatha and ANC supporters in Thokoza township, east of Johannesburg, according to a police report.

Fears of increased violence by white extremists rose sharply today after a leader of the far-right Conservative Party, Koos van der Merwe, told white gold miners in the town of Welkom in Orange Free State province to take guns underground as protection against blacks following the killing of a white miner there last week.