THE best thing about Headquarter House, destined after yesterday's agreement to be the residence of China's military supremo in Hong Kong after 1997, is that ''no one can look down on you'', according to its present high-ranking resident. The Commander British Forces, Major-General Sir John Foley, last night said his exclusive Peak residence was so secure and secluded there was no chance of anyone peeping in. News that his drawing room, with its real log fire and wooden floors, would probably become the domestic focal point for the newly arrived chief of the People's Liberation Army came as no surprise to Sir John. He said HQ was a ''comfortable, happy house, ideal for a family''. The Foleys in No 11 are neighbours of the Chief Secretary, the US Consul-General and other notable Barker Roaders. In their two years at HQ they gained a reputation for hosting enjoyable, if rather militarily formal, parties in the impressive dining room. Prominent party-going businessman David Tang said he had been invited to several affairs at No 11. ''This is probably the most magnificent house in Barker Road; I've been to some good 'military' dinners there. The atmosphere was rather like being in the officer's mess at Sandhurst.'' Simon Murray, regional president of Deutsche Bank, said one was unlikely to forget that this was military land: apart from two stone lions there is a Gurkha guarding the gate and the Union Jack flutters on the flagpole. ''But under the Foleys it has taken on more of a family atmosphere.'' The Foleys said most of their entertaining had been dinner parties for less than a dozen people: the biggest event was last Monday, when more than 100 came to a party marking the end of their posting in Hong Kong. ''The trouble is, with that number of people in the house, the air-conditioning couldn't cope,'' Sir John said. The modern five-bedroom house was designed in 1979 by a Chinese architect who won the contract in a competition. The half-hectare site has no swimming pool or tennis court, but there are spectacular views over the harbour. And unlike the Governor's residence below in Mid-Levels, the view is not blocked by the Bank of China Tower.