PORT ELIZABETH, South Africa (AP) _ Non-white workers at the General Motors plant said they were thrilled Monday about the U.S. company's challenge to race segregation on city beaches.

The company announced Thursday that it would provide legal aid to the 1,800 black, mixed-race and Asian workers at its only plant in South Africa if they were prosecuted for using any of the city's whites-only beaches.

Some workers vowed to defy the city ban by bathing in front of the whites- only signs.

''I don't see why I can't ... The beach doesn't belong to anybody. That's God's sea,'' said Patrick Mazantsi, a 37-year-old black security guard, as he ended the day shift.

''I've decided to go this weekend to King's Beach (a popular whites-only beach), and take my family, and see what happens,'' he said.

Gordon Booth, 40, a mixed-race data processor at the plant, said, ''I think it's a great step ... I'm a swimmer. I'm going this very weekend to King's Beach. If I'm arrested, I've got my boss behind me. They can't arrest me for using God's gift.''

The controversy began last week when GM's managing director in South Africa, Robert A. White, told the city council the company would help defend any non-white employee prosecuted for using white beaches.

White noted in a letter sent to local newspapers that other cities had desegregated beaches but ''it seems the council has neither the courage to do so nor the integrity to deal with the issue urgently and openly.''

''General Motors finds the existing ordinance abhorrent,'' he wrote.

In Detroit, GM public affairs manager Michael G. Killeen said White simply wanted to encourage the city council to open the beaches, and ''it was not his intention to encourage people to break laws ... but to make the city council sit up and take notice.''

Only a few whites - and no blacks - ventured Monday into the blustery offshore wind on King's Beach, where the ''whites only'' sign is in three languages - English, Afrikaans and Xhosa, the black tongue.

Among those who did was Hannes Fouche, who said he favored beach segregation.

''They should give them a beach and say, 'That's your place, do what you like,'' he said.

Port Elizabeth has four beaches for whites, two for the mixed-races and one for blacks. Durban and Cape Town, the other major coastal cities, abolished beach segregation in recent years.

On Saturday troops deployed in armored cars at King's Beach, but Defense Minister Magnus Malan told Parliament Monday they were there as ''spectators.'' U.S. companies have broken new ground here by recognizing black trade unions, trying to eradicate apartheid and give workers housing and job training.

But the GM action is the first by any foreign-based company pledging support for employees who defy an apartheid law. Business Day, Johannesburg's respected financial daily, said that although many people would see the move as interference in South Africa's internal affairs, it should be praised as ''a positive contribution to the process of change.''

A city council subcommittee has recommended beach inspectors call in police to arrest violators if non-whites refused to leave a white beach. That decision is up for review Thursday by the full council, and the vote is expected to be close.