PROPERTY consultants believe the Government's 70 per cent mortgage ceiling was responsible for a 16.2 per cent tumble in January-to-June building unit deals. According to the Land Registry, there were 62,791 sale and purchase agreements during the first six months of the year, 16.2 per cent fewer than during the first half of last year. However, there were 4.1 per cent more deals than during the second half of last year. The total amount involved in these agreements was $157.86 billion. This represented a drop of 5.1 per cent compared with the same period in 1992. Property consultants attributed the decline to the Government's attempt to cool speculative activities by the recent implementation of stamp duties on property transactions and a 70 per cent maximum mortgage lending limit. ''The Government's efforts to cool speculative activities has slowed down buying activities,'' said Jones Lang Wootton residential department director Clara Chan Ka-ling. According to Mrs Chan, the Government's clampdown on speculative activities had also affected the sale of smaller residential units. She said: ''With the 70 per cent maximum mortgage ceiling, buyers of smaller residential units, which cost up to $3 million, had to come out with 30 per cent of the downpayment, which amounted to about $1 million and many of them could not afford that money. ''It affected their affordability, leading to a slowdown of sales of smaller residential units.'' First-time home-buyers were particularly hard hit because they had to come up with more money to own and to furnish their new home. Mrs Chan said the Government's moves had not had much effect on luxury properties, however. ''Buyers of luxury properties in general tend to have the money to afford such properties and were generally not affected very much by the Government's actions,'' she said. Mrs Chan said there had been active buying of homes last year, with the prices of smaller homes rapidly catching up with those of luxury properties in terms of square footage. ''The price of smaller residential units per square foot was catching up with luxury properties and that didn't make much sense as luxury properties traditionally cost more as they were better located, had higher land cost and also had better furnishings,'' she said. However, she noted that prices of luxury properties had since picked up. Richard Ellis director David Runciman said the market had ''more or less'' hit its peak. ''What you see now is a slowdown as a result of the tightening of credit,'' said Mr Runciman. The total amount secured under mortgages, apart from building mortgages, was $48.3 billion, an increase of 21.9 per cent compared with the second half of 1992 but a decrease of 1.2 per cent compared with the first half of last year. The total number of property owners rose by 2.4 per cent from 1,469,604 in June 1992 to 1,505,003 in December 1992, and again by 1.8 per cent to 1,532,459 in June 1993.