SALES of flats under the Housing Authority's Home Ownership Scheme could grind to a halt as early as the middle of next year if the Sino-British Land Commission remains paralysed by the impasse over the Governor's constitutional reform package, a senior Housing Department official admitted yesterday. But the assistant director of housing, Mr Marco Wu Moon-hoi, denied reports that the row would halt the programme in the 1993/94 financial year. A more immediate threat was to the allocation of six hectares for the Government's proposed sandwich class housing scheme. A spokesman for the Planning, Environment and Lands Branch said no work could go ahead on the 5,000 Housing Society flats to be built under the scheme, until the Land Commission had agreed on the land sales programme for the new financial year. However, he said the Land Commission dispute should not affect the $2 billion ''fast-track'' portion of the sandwich class scheme, allowing eligible home-buyers to purchase subsidised properties on the open market, until the new purpose-built units come on stream. Normally, the Land Commission would meet towards the end of March to discuss land releases for the coming year. But China has refused to set a date for a meeting and Chinese team leader Mr Sun Yanheng last week said he could not imagine the work of the commission would not be affected by the Sino-British dispute. A halt in land sales would punch an estimated $12 billion hole in the Government's estimated revenues for this year and cut an equivalent amount from the special post-1997 Land Fund set aside for the Government of the future Hongkong Special Administrative Region, which automatically receives 50 per cent of the takings from land sales. A long delay could also hit the release of 46 hectares for China Light and Power's $60 billion expansion plan at Black Point. Meanwhile, land approved for Container Terminal 9 under the 1992/93 programme will have to be resubmitted to the commission unless all the details are formally agreed with operators before the end of this month. Mr Wu said there was no problem over approximately 13,000 Home Ownership Scheme flats due to be sold in 1993/94 as the Housing Authority was already in possession of titles to the land. But the big question mark hung over some of the 14,000 units due to go up for sale the following year. While sales for April 1994 were secure, the Land Commission would still have to give the go-ahead for land titles to be granted on blocks due to come on the market in August and December 1994. He said the dispute would not affect construction plans, as the Buildings and Lands Department needed only an Advance Possession Licence to go on site. These were traditionally granted before the Land Commission was consulted. The same system will not apply to sandwich class housing, which will be built by the Housing Society. Unlike the Housing Authority, it will require titles to the land before it starts building, so the release of the land will need Chinese approval.