Your grocer is smiling. It's not a wide grin, but a discernible look of pleasure was painted on his face yesterday at the opening of the annual Food Marketing Institute here.

Spokesmen for the supermarket industry and their public opinion pollster took a generally upbeat approach in the "state of the industry" briefings. They cited increases in consumer spending and consumption during 1976 and a lessening of the inflation rate as reasons for "a general upturn in performance" that should lead to a "steadily healthier, increasingly profitable food industry."

Statistics they use showed average store sales up 6.5 per cent last year. The inflation rate for food at home was 2.1 per cent in contrast to 8.3 per cent in 1975 and 14.9 per cent in 1974. Wages increased, but at a lower rate than in any of the last three years.

There were signs of a lessening of tension with consumers. According to Ruth Clark of Yankelovich, Skelly and White, the firm that does public opinion research for FMI, 92 per cent of the public experts further food price increases and only 10 per cent now blame the supermarkets for current high prices.

But the retailer isn't altogether out of the woods. "The climate of mistrust and suspicion continues," White reported. The survey found 61 per cent "feel that supermarkets strike a bad balance between profits and corporate responsibility." Oil companies, business in general and food manufacturers fared worse; but banks, farmers and neighborhood groceries did better.

Also, while the number of consumer activists stayed relatively stationary - at 10 per cent - another 40 per cent, a sharp increase, now considered potential activists. This means, White said, consumers are "more vocal but not necessarily more committed."

An outlook report confirmed several previously reported food supply trends: less beef at higher prices, more pork and dairy products on the market, a leveling out of fruit and vegetable prices after dislocations caused by winter cold.

Eugene Gerke, an FMI economist, said the California drought, while serious, is not yet causing supply disruptions and probably won't this year. He reported a sizeable decrease of coffee shipments and an increase in tea shipments during four-week period early in the year, but said there was not yet enough evidence that this trend would continue. The current forecast is for 4 to 6 per cent food price inflation this year with coffee, cocoa and other imports receiving much of the blame for the increase.

On Sunday evening, Esther Peterson was presented with FMI's first Industry Statemanship Award. She is a special assistant to the President for Consumer Affairs and served in a similar position for President Lyndon Johnson. For the past six years she has been consumer adviser to the Giant Food chain in Washington.

Until this year the industry gathering here was known as the Supermarketing Institute (SMI). With the amalgamation earlier this year of its two sponsors, the Grocery Manufacturers of America and the National Association of Food Chains, the name was changed to Food Marketing Institute. Scarcely anyone among the thousands at the convention center here appears to have noticed.