The outlines of a plan for the future of Hong Kong have begun to emerge from talks in Peking between Britain and China. The plan, flowing essentially from Chinese proposals during the top-secret negotiations, rests on three legs.
* Britain would agree to surrender to China sovereignty over Hong Kong, now a crown colony, when the lease on the so-called New Territories runs out in 1997.
* In return, China would allow the administration of Hong Kong to continue on something like the present basis, probably with participation by local Chinese and minimal disturbance to the high-energy capitalist economy of Hong Kong. (Hong Kong is now ruled by a British-appointed governor aided by an Executive Council.)
* If a suitable future administration is agreed upon, China will retain the right on, say, eight or 10 years' notice to absorb Hong Kong as part of the People's Republic.
It is emphasized in Whitehall that the present round of talks, following a deadlock of six months, has produced no hard and fast formula. But diplomatic sources are saying both sides are showing realism about the need to achieve agreement soon.
The three-element formula will be considered further in talks next week. It is thought to be one which will give China a valid claim to sovereignty while enabling Hong Kong to continue as a vibrant banking and business center.
The formula is thought to satisfy Peking and London. The third point, giving China the right to claim Hong Kong completely and ask the British to leave, would be unlikely to be invoked if other parts of a settlement worked successfully.
Whitehall sources say the Chinese seem prepared to bend communist rules to enable Hong Kong to continue as a capitalist haven under the nominal tutelage of Peking.
The New Territories, covered by a treaty that will expire in 14 years, constitute the bulk of Hong Kong. Separate perpetual treaties cover Hong Kong Island and the district of Kowloon. Britain accepts that, without the New Territories, the rest of Hong Kong would not be viable as a business or administrative entity. China in any case insists that all Hong Kong treaties are ''unequal'' and invalid.