RESIDENTIAL flat sales increased by 33.6 per cent in March from February, as three major developments came on stream to help bring total sale and purchase agreements to 11,678. The Registrar-General, in Land Registry figures released yesterday, said the total value of the agreements was $23.87 billion - a rise of 29.7 per cent on the previous March. The three developments which triggered the sharp increase were Saddle Ridge Garden and Sunshine City, in Ma On Shan, and Park View Garden in Sha Tin. Sector specialists said Saddle Ridge Garden was developed under the Government's private sector participation scheme, while Park View Garden and Sunshine City were both developed by Henderson Land. The February home market was also buoyant, with 8,739 sale and purchase agreements registered, more than double January's total. The long-running Sino-British row on Hongkong's political reforms was blamed for dampening the local residential market in January, when only 4,250 sales and purchase agreements were registered. Government figures for March show there were six building mortgages and 9,272 other mortgages registered, compared with 10 and 11,509, respectively, in the same month last year. The total amount secured under new building mortgages in March was about $1.18 billion compared with about $200 million in March 1992. The total amount secured under new mortgages, other than building mortgages, rose by 0.9 per cent from about $5.15 billion in March last year to about $5.2 billion in March this year. Repayments under mortgages of all kinds, as evidenced by discharges and mortgagee's receipts, increased by 19.4 per cent from about $2.41 billion in March last year to about $2.88 billion in March this year. Vickers Ballas associate director Adrian Ngan Wai-hung said yesterday there were plenty of residential projects in Hongkong in the short term, with an active market boosted by the favourable response to recent property developments on offer. Residential projects on sale this month include phase four of Ap Lei Chau's South Horizons, the Ma On Shan Centre in Ma On Shan and Sea Crest Villa in Sham Tseng. Mr Ngan anticipated strong demand for flats because major developers were offering mortgages of up to 85 per cent of flat valuations. He added: ''Most of the major developers have cut prices for flats recently by more than 10 per cent, and there was a demand there.'' The sweetened offers proved attractive to local home buyers, who had shown keen interest in the local market, he said. This positive response had, in one way or another, shown that the residential market had bottomed out after months of gradual decline, he said. Mr Ngan played down the impact on the local property market of the outcome of the Sino-British talks on Thursday but he appeared optimistic about the property market. ''Any outcome of the talks might not have any real direct effects on the market,'' he said.