One-fifth of British companies operating in South Africa have pulled out over the past two years, deterred partly by falling profits, the anti-apartheid movement reported Monday.

But the movement said the flurry of British withdrawals follows the same pattern as an earlier spate of U.S. pullouts, with most companies retaining commercial links and with their products still available.The report, The South African Disconnection, said the number of British companies with subsidiaries or affiliates in South Africa has fallen to 235

from 297 in the past two years, while 19 others have cut operations substantially.

Report author Stuart Bell said Britain remained the biggest foreign investor in South Africa, but the value of direct British investment has fallen from 6 billion (US$11 billion) in 1980 to an estimated 2.9 billion (US$5.4 billion) in 1986.

The big British names that have left South Africa in the past two years include Barclays Bank, Legal and General Insurance and the Rover Group PLC.

It's definitely a success, Mr. Bell said in a telephone interview.

but there are caveats. Many of the companies, like the American corporations that pulled out, continue to have commercial links and have negotiated franchise arrangements. However, we were quite surprised by the scale of British pullouts.

About half of the former foreign-owned companies have been bought by South African companies, such as Barclays and the U.S. Ford automaker that were bought by the Johannesburg-based mining giant, Anglo American Corp. Nearly 30 percent were bought by local managers.

Extracts from the report, due for official release next week, were published Monday in the Financial Times and confirmed by Mr. Bell. The anti- apartheid movement is one of the world's oldest and largest organizations battling apartheid in South Africa.

The report said departing companies seldom cite opposition to apartheid or the impact of anti-apartheid lobbies as official reasons for leaving, but mention instead industrial logic and strategic requirements.

However, British executives of companies with high profiles in South Africa have cited what some call the hassle factor - being targeted by demonstrators or boycott campaigns. They say it is simply not worth it for the small percentage of total business done in South Africa.

Records kept by the Associated Press in Johannesburg show that 113 U.S. companies have withdrawn from South Africa over the past two years, with some 160 remaining.

Most withdrawals, except Eastman Kodak, have left the products, designs and parts - for example, Coca-Cola and IBM - still available in South Africa.

We recognize the limitations of disinvestment, said Mr. Bell.

But he said disinvestment was having an impact by drying up capital investment, encouraging highly skilled white emigration because of lack of opportunities and making the longer-term availability of products uncertain.

The British Industry Committee on South Africa, a private organization which represents companies that account for 75 percent of Britain's $637 million annual trade with South Africa, did not dispute the anti-apartheid movement's report.