General Motors Corp. came under the fire again yesterday for its operations in racially segregated South Africa as about 50 protesters tried to force their way into the company's annual meeting.

The demonstrators were headed off by the police at the Fisher Building auditorium here without arrest or injury, but some shareholders inside accused the automaker of being in league with the South African government.

Chairman Thomas Murphy defended GM's operations in port Elizabeth, where the firm employs about 3,600 workers. "We deplore apartheid," Murphy said. "We are trying by peaceful means to be a positive force in South Africa.

Murphy told the approximately 700 stockholders attending the session that the company would hold executive salary increases below 5 percent this year in line with president Carter's anti-inflation requests. He said the total salaries of corporate officers as a group would not rise by more than 5 percent and that executive committee members' salaries would not rise by more than 5 percent each. Bonus increases would follow the rule also, he said.

Labor costs for unionized workers will continue in the area of 10 percent in 1978, he said.

He stood by his forecast of industry sales of 15.5 million cars and trucks this year, obviously taking some pleasure in pointing to the current record pace of sales. He said the high volume is being set despite the blizzards of January and February, a long coal strike, and "a good deal of skepticism on Wall Street."

Mandated safety and emmissions controls since 1968 have added $666 to the price of every new car, according to a congressional study, he said. GM estimates that federal safety, emissions and fuel economy standards in the early 1980s will "add another $800 or more to the average price of our cars," he said.