WHEN Lady Lydia Dunn announced she would leave Hong Kong for London later this year, it sent ripples across the British territory.
An integral part of Hong Kong's elite and daughter of a prosperous Chinese family, Lady Dunn said her move did not indicate a lack of confidence in the future of the territory, set to become part of China in less than two years. But Hong Kong's ''Iron Lady'' - who sits in Britain's House of Lords and serves as adviser to the governor - is symbolic of a historic shift.
Power here is passing from the Anglo-Chinese elite to a more eclectic, ''Sino-fied'' business establishment. And the old British trading companies, or hongs, are preparing themselves for rule by Beijing after 1997.
Power Shifts in Some British Firms to Hong Kong Chinese
The shift can be seen on many levels. The Hongkong and Shanghai Banking Corporation (HSBC), for example, is probably the single most important business in the colony. It has been conducting a ''colonial audit'' of its once-fabulous collection of Chinese art, replacing older paintings with works from contemporary Hong Kong artists.
''We felt the collection was not appropriate in a modern Asian setting,'' says Pamela George, a spokeswoman for the bank. Many paintings featured scenes from the opium trade or of Europeans with their Asian servants.
At a deeper level, the bank has been actively diversifying its business away from Hong Kong for a decade. In 1987, it bought the Marine Midland Bank, giving it a foothold in the United States, and then it acquired Midland, one of England's four clearing banks. The parent HSBC Holding is now domiciled in London and regulated by the Bank of England.
In moving legally to London, the Hongkong Bank is simply following a trend. At least half of the publicly listed companies in Hong Kong recently have taken the precaution of moving their nameplates abroad, usually to Bermuda or the Cayman Islands.
''The fact that they have done so represents a very substantial nervousness about the future,'' concedes Jimmy MacGregor, the General Chamber of Commerce's representative in the territorial legislature.
It is still unclear whether China will permit ''The Bank,'' as it is sometimes called, to maintain its commanding position after 1997. Already the Bank of China, whose gleaming new headquarters dominates the skyline, issues some of Hong Kong's bank notes.
''Bit by bit, the Bank of China will move into a more dominant position, and the Hongkong Bank will give way gracefully,'' predicts Mr. MacGregor.
He adds that many of the executives in companies that have moved to offshore domiciles feel assured about their prospects and have made substantial investments in China. But they also want to protect their shareholders against the remote threat of sequestration or expropriation.
Looking back over the past 10 years, MacGregor says that the hongs' ''absolute contribution to the economy of Hong Kong has increased, but the proportion has decreased because the world has poured into Hong Kong to take advantage of the opportunities in China.''
The influx has included other British-owned concerns, such as the department-store chain of Marks and Spencer, which has no historical associations with Hong Kong and expects to compete on an equal footing with the other multinationals here without special privileges.
Most of the British trading companies are still headed by Europeans, although localization (promoting Chinese to senior positions) is proceeding in the business community as it is in the government. Companies such as Inchcape, Hutchinson Whampoa, and Hong Kong Telecom all have Chinese chief executive officers.
Europeans still firmly control Jardines Matheson Company, which in some ways is the odd man out among the British concerns here. It moved its legal address to Bermuda in 1984, the same year that Britain and China signed the Joint Declaration on how Hong Kong would be returned to mainland rule. More recently, it has completely delisted its shares from the local stock exchange. The owners, the Keswick family, who reside in Britain, publicly endorsed Hong Kong Gov. Christopher Patten's democratic reforms, while the other hongs, mindful of Beijing's strong opposition, maintained a studied silence.
''Jardines lives with an unfortunate past,'' says MacGregor, referring to the company's history as an opium trader and an instigator of the 19th-century Opium War against China. ''It has become a soft punching bag for Beijing, which feels it has to expiate old sins.''
Nonetheless, there are few signs that the company, made famous by the novel ''Noble House,'' has any intention of pulling out of Hong Kong soon. And as long as the company's Noon Day Gun goes off, it will maintain its involvement in the territory.