TENANTS on public estates may face tough tenancy contracts barring them from buying private flats under a package of Housing Authority proposals aimed at helping curb runaway property prices. Authority members and senior housing officials are to explore ways to speed up flat supply at a special closed-door meeting today at the authority's Ho Man Tin headquarters. The marathon session, scheduled to last at least six hours, was ordered by authority chairman Rosanna Wong Yick-ming amid government initiatives to combat rising flat prices. Members agree that increasing the supply of rental and Home Ownership Scheme flats is the best the authority, as a public sector housing supplier, can do. One major item on today's agenda is to fix policies to deal with tenants owning private flats elsewhere, and tightening tenancy contracts to restrict rental-flat tenants buying flats. Among the proposals is to add provisions to new tenancy contracts requiring tenants to seek the authority's approval if they want to buy private flats, or forbidding them buying flats in the first five years after moving into a rental unit. A more radical option is to amend existing contracts to chase out those who own units elsewhere. Members are not expected to vote for a particular proposal but will fix a guideline policy for future discussions by the authority's sub-committees. Member Leung Wai-tung said she believed that suppressing tenants' demand for private units could help curb the upward pressure on prices. ''A tenant with a government unit has no urgent need to buy private flats. If we can stop them entering the market, it can at least help slow the rising trend of prices.'' Fellow member and legislator Frederick Fung Kin-kee agreed but said he would oppose any amendments to existing contracts. ''I would support adding restrictive conditions to new tenancy contracts,'' he said. An authority survey last year found that 13 per cent of the 600,000 tenants owned at least one flat elsewhere, leaving their rental flats idle or using them as store rooms. Some tenants owned up to five flats. It also found that tenants accounted for a quarter of private unit transactions between October 1992 and March last year. Another aim of the discussions is to determine a new type and lower-price Home Ownership Scheme flat for those hit by government clearance or redevelopment. A failed policy to sell rental flats at low prices to sitting tenants is expected to be raised again. The authority's nine sub-committees, based on the outcome of today's special meeting, will work out details and finalise proposals at the authority's full meeting in late June. Other items for discussion are: Increasing the amount under the authority's Home Purchase Loan Scheme, which now stands at $200,000; Reviewing building density on existing sites to allow more flats to be built without additional land; Reducing the time needed for ''document travel'' between government departments when seeking building approval for rental sites; Allowing private developers to take a bigger role in building Home Ownership Scheme estates to speed up supply.