NEW YORK, JUNE 17 -- ITT Corp. today became the third major U.S. company this week to announce plans to withdraw from South Africa amid signs that political conflict in the white-ruled nation has made it impossible to do business there.

ITT said it had sold its only wholly owned South African subsidiary, an automobile brake maker, to Glasfin Investments Ltd., a South African company, for about $3 million.

ITT said the facility, Alfred Teves Engineering (S.A.) Ltd., has about 300 employes, of whom "the great majority" are black.

On Sunday, Ford Motor Co. said it would donate the bulk of its 42 percent interest in South African Motor Corp. to the company's employes, most of whom are black.

On Tuesday, Citicorp, the last U.S. bank operating in South Africa, announced the sale of its unit there to First National Bank of Southern Africa Ltd. for about $39 million.

ITT, which has interests in telecommunications and electronics, consumer products, natural resource extraction and insurance and finance, also said it was proceeding with divestiture of minority interests in two other businesses.

They are a 16 percent stake in Maister Directories Ltd., a yellow-pages advertising business, and a very small, "passive" investment in South Atlantic Cable Co., which makes telephone cable.

ITT said its South African interests accounted for only 0.1 percent of its revenue last year.

An ITT spokesman said the company sold another South African subsidiary, Supersonic Radio and Television S.A., to local interests in 1985.

In a statement today, ITT Chairman Rand Araskog said: "We have always believed that the presence of U.S. corporations, and ITT in particular, has provided a positive force for social change in an extremely troubled environment. But, despite the efforts by ITT and other U.S. corporations in supporting the Sullivan Principles, the environment in South Africa is no longer conducive to continuing our business operations."

The Sullivan Principles are a set of guidelines for U.S. companies operating in South Africa. The Rev. Leon Sullivan, pastor of the Zion Baptist Church in Philadelphia who developed the principles, recently abandoned the guidelines, saying all American businesses should withdraw from South Africa and a total U.S. economic embargo should be imposed.