ANALYSTS expect Hang Seng Bank to report an increase in interim results of between 22 per cent and 40 per cent tomorrow. The wide range of forecasts is attributed to differences of opinion on how proceeds from the sale of Wing On Bank will be treated. Some analysts believe the proceeds should be entered as an extraordinary item, others that they should appear above the line in the profit and loss account. Apart from the Wing On gain, the bullishness rest on the assumption that last year's big provisions against loans to Canadian property developer Olympia and York (O & Y) will not be repeated. ''Hang Seng is a fairly conservative bank. Over O & Y, the bank might have written off as much as possible last year,'' Jardine Fleming investment analyst Steven Li said. Hang Seng's exposure to O & Y was US$100 million, but the bank refused to disclose the level of provisions made last year. Forecasts for the growth rate of mortgage loans and trade finance has also influenced analysts' predictions. ''Though the overall mortgage loan market has slowed down, it recorded a growth rate of 13.5 per cent compared with 30.5 per cent last year,'' Salomon Brothers banking analyst Alvin Chong said. ''Trade finance growth rate matches with the increase last year on a year-on-year basis, around 13 per cent. It is slowing down, but it is growing.'' However, analysts predicting slower profit growth think otherwise. ''Both the mortgage loan and trade finance will grow at around 10 per cent only,'' one said. Credit Lyonnais regional banking research director Laura Grenning said: ''The growth in the margin and size in trade finance and corporate lending is not sufficient to offset the slowdown in mortgage loans.'' This was because mortgage lending constituted more than half of Hang Seng's loan portfolio, whereas trade finance only accounted for 25 per cent. Mr Chong said the bank, as a net lender of Hong Kong dollars in the inter-bank market, would benefit from an improved profit margin from that part of the business.