A rise in food prices, a sensitive issue in Poland, where past attempts at increases have sometimes led to riots that toppled communist party leaders, is planned for early next year according to a senior Polish official.

At a press conference for Polish journalists, government spokesman Jerzy Urban disclosed that food prices "most probably" would go up "moderately" near the start of 1985. He said the increases would coincide with an end to the rationing of most foods, except for meat and chocolate, and were necessary to modulate the demand for food and to compensate for the higher procurement prices being paid by the government to farmers.

"Food price increases could be avoided only by increasing the state subsidies," said Urban, according to a text of yesterday's press conference published today. "Such subsidies could be financed only by increasing the prices of industrial consumer goods more than presently planned. This measure would be difficult to accept from both the economic and social points of view. There is no other way out but to increase the prices."

Food price increases, along with a shortage of meat, triggered serious worker demonstrations in 1970, 1976 and 1980, and led to the fall of Polish leaders in 1970 and 1980. In 1980, the resulting political unrest gave rise to the Solidarity union movement.

Under the straitjacket of martial law that ended Solidarity, the government was able in early 1982 to impose enormous increases in food prices in the range of 100 percent or more. Much more moderate price rises were introduced at the start of 1983 and 1984, without drawing violent protest.

Mindful of the political repercussions of price rises of the past, Polish authorities preceded the 1984 increases with a novel effort at consultation with society. Several alternative packages of price increases were floated publicly and people were invited to comment on them. Most of the response was critical of all the possibilities offered. After delaying the increase, the government eventually ordered increases that were significantly less than initially projected.

Urban indicated that some form of consultations would be tried again before the 1985 food price jumps take effect. But he said the discussions could only be about general categories of products, not individual items.

"The consultations could cover certain groups of products," he explained. "But we cannot ask the public whether, for instance, butter should be cheaper or more expensive. Asking such detailed questions is not what consultations are about."

According to official figures, the consumer price index is up 16 percent over last year, exactly as planned. In March, the government banned price increases for most consumer goods and set a 10 percent ceiling on the prices producers could charge.

But workers' incomes have risen 20 percent on average. Because wages have gone up at a faster rate than prices, Urban said, new price increases had become a necessity.

"Nominal incomes continue to grow," he said. "Without price increases, food would become relatively cheaper, demand would increase more quickly than production and we would end up with empty shelves." He said the rate of inflation expected in 1985 is 9 percent.

Many Poles appear to have accepted the principle that prices must be allowed to rise periodically if the country's heavily planned economy is to operate more like a freely competitive market. But they do not like the reality of it.

The increases of the past few years have been portrayed by the official press as part of the government's overall effort to reform the economy by bringing prices closer into line with actual production costs so that inefficient subsidies can be phased out. But the only evidence of reform felt by the average Pole so far has been higher prices.

Many basic consumer goods -- furniture, household appliances, cars -- still require years of waiting and involve a tremendous expense in relation to what an average worker earns. Some basic food items -- meat, butter, flour, rice and sugar -- are still rationed. To get additional supplies, Poles shop on a thriving black market, where prices are higher.

Some of the economic pressure on the government was relieved this year by a good harvest, particularly in grains and potatoes. But Urban said domestic yields would still not be sufficient to cover needs for grain and vegetable fats.