THE size of loans in the sandwich class home purchase scheme may be increased because of spiralling property prices over the past few months. This is one of the proposals being considered by the Government in a review of the $2 billion loan scheme to help middle-income families buy their own homes. The first phase, in which a successful applicant is offered a loan of up to $500,000, was launched last August. So far about 200 families have been granted money to buy flats. The second phase is expected to be launched in July after a review. The Government has taken note of the loss in real value of the $500,000 loan as market prices have jumped by almost 20 per cent since last August. Leo Kwan Wing-wah, the Deputy Secretary (Housing) of the Planning, Lands and Environment Branch, said there were plans to increase the loan amount to ''reflect the market price rises'' but he refused to specify an amount or give details. ''We also have plans to relax a rule to allow families to buy flats of up to 15 or 20 years old,'' he said. The current rules restrict families to buying flats less than 10 years old. According to the latest proposals, eligibility rules will be tightened to limit easy access by owners of overseas properties to the scheme. Mr Kwan said the Government was weighing up two options. ''One option is, simply, to disallow property ownership of any sort. The other is to count it as the applicant's asset and we may disqualify him if his assets have reached a certain level,'' Mr Kwan said. He added the Government was trying to fix the definition of overseas properties. ''For example, whether an owner of a house on the mainland which he inherited from his clan should be viewed as his overseas property. Obviously he does not live there and the house may be too old to live in.'' Legislator Frederick Fung Kin-kee agreed that exemptions be given to this particular group but he said the loan amount should not be increased. He said it would become a bottomless well if they were to raise loans to chase rising property prices. Leung Kwong-cheong, a spokesman for the Hong Kong Association for Democracy and People's Livelihood, said the Government should find ways to stabilise property prices rather than increase the amount of loan. The loan scheme will last until 1996 when a long-term flat sale programme will be launched.