CHEAP food helped rein in inflation last month, with the Consumer Price Index (A) - the most commonly used barometer of prices - down at 7.9 per cent. But the Government warned that typhoons which hit the territory in late September had already triggered a surge in the price of fresh vegetables. A spokesman said: ''The slower increase in the CPI (A) in September was mainly due to more moderate rises in the prices of fresh vegetables and in rent for housing. ''However, there were indications that the prices of fresh vegetables surged significantly in early October.'' Economists say the September figures - the lowest since April - suggest the Government has taken an overly conservative stance in forecasting an annual rate of nine per cent. It is the third time this year that inflation has fallen below eight per cent. In April, price rises fell to a five-year low of 7.7 per cent. CPI (A) covers households spending less than $10,000 a month. The bigger slice of spending on food in less well-off homes saw trimmed price rises filter through to the CPI (A) rates more handsomely than in wealthier households, where inflation was a hefty 9.2 per cent. Taking the first nine months together, the year-on-year rate of increase averaged 8.4 per cent. Jardine Fleming Brokering economist Daryl Ho Hon-kit said: ''If they want to achieve nine per cent for the whole year, as the forecast stands, you are talking about around 10.8 per cent for the remaining months of the year, and that's very unlikely.'' The CPI (B), covering families spending between $10,000 and $17,499 a month, rose by 8.1 per cent in September, while the upper level Hang Seng CPI (for those spending between $17,500 and $37,499 a month) maintained the 9.2 per cent rate in August. The composite CPI, which measures the income groups covered by the three other indices, was up 8.3 per cent. The head of economic research at the Bank of East Asia, Benjamin Chan Sau-san, said: ''While CPI (A) has dropped, the Hang Seng CPI rate has been maintained at 9.2 per cent, because of the food weightings. ''But if you exclude food items, inflation on core items is still at a very high level and has been maintained at around nine per cent for several months. ''Food items are very important. Growth for this year has been substantially lower than last year and the weighting of food is very large in CPI (A) - 41.2 per cent.'' Externally, inflation has been cut by the depreciation of the yuan. Fresh foods imported from China make up around six per cent of CPI (A)'s construction.