Canada's cheap gas: don't forget a calculator

If you're planning to save money by buying gasoline in Canada these days, take along a slide rule or pocket calculator to add up your bills.

So advises Norman Grapes, executive director of the United Gasoline Retailers of Western New York Inc.

Over the last several years, many US motorists approaching the border from the Buffalo area have looked forward to paying less for gasoline in Fort Erie, Ontario, because of Canadian government price controls on gasoline.

Now many of them are not only being disappointed by the prices at some Canadian service stations, but getting thoroughly confused as well. In fact, some US motorists claim they have been the victims of a kind of fraudulent ''shell game'' in which prices seem to be cheaper but are not - once the US-Canadian exchange rate is factored in.

Mr. Grapes somewhat reluctantly admits, however, that US motorists can still save money by buying Canadian gasoline. For example, if a US motorist buys the equivalent of 15 US gallons in Fort Erie, he or she can save approximately a dollar in US currency. In Grapes's opinion, this savings is negated by the time and trouble it takes to cross the border.

Many motorists obviously don't agree and are still crossing either the bridge here into Canada or the Rainbow Bridge in nearby Niagara Falls for gasoline ''bargains.'' But last fall the Canadian goverment of Prime Minister Pierre Trudeau went a long way toward ending controls on gasoline and the long lines of US gasoline bargain hunters that used to form every day on these bridges are seldom seen.

Unlike gasoline sold by the gallon in the US, Canadian service stations sell it by the liter (one US gallon is 3.785 liters). Simple enough, you say? Well, after calculating the amount in liters, there's the not-so-simple matter of figuring the US-Canadian dollar exchange rate.

As of this writing, the US dollar is the equivalent of $1.27 in Canadian currency. Some service dealers have complicated things by offering a better than 27-cents-on-the-dollar exchange rate - some as high as 40-cents-on-the-dollar. So you also have to change US money into Canadian.

But don't put away your calculator yet. The exchange rates service stations offer may vary daily with the fluctuation of the official government bank rates. And you have to find out how the service station dealer is calculating his exchange rate. Is he basing it on the total amount of American dollars you hand him? Or, if you don't have the exact change, is he giving you the exchange rate only for the actual price of the gasoline - and not on the change?

Grapes is not saying that the majority of Canadian dealers are committing outright fraud. But he says that while prices may seem low on the surface, upon closer examination they are found to be just a little under US prices.