The blunt rejection by Poland's official trade unions of government plans to raise food prices next month has left communist authorities little choice but to put off the planned increases and prepare another approach, western diplomats and Polish analysts said today.

Leaders of the trade unions condemned the price proposals at a meeting yesterday, calling them ineffective against the country's economic crisis and damaging to living standards -- charges that also have been voiced by Solidarity leader Lech Walesa and members of Poland's political opposition, who usually do not agree with the new unions. These were set up by the government in 1982 to replace the banned Solidarity union.

Increases in the cost of food long have been an explosive issue in Poland. Previous attempts to raise prices led to riots or strikes that toppled communist party leaders in 1970 and 1980. Hoping to bring about advance national agreement this time, Polish officials preceded the planned increases by offering several options and inviting public comment.

Three plans were published containing varying scales of price increases. Among the key proposals: sugar could rise by up to 73 percent, flour up to 41 percent and butter up to 25 percent. In return, said the government, the rationing of these items would be ended.

A 15-minute nationwide strike has been called for noon Thursday by Walesa and Solidarity underground leaders to protest the price increases and longer working hours also being sought by the authorities.

Labor Minister Stanislaw Ciosek said on television this evening that the Cabinet would meet Monday to decide whether to proceed with the price inceases, giving "special attention" to the position of the official unions.

The government modified food price rises last year after somewhat more muted criticism from the unions. By showing itself responsive to pressure from the official groups, the government hopes to reinforce the credibility of the unions, which now claim about half the 10 million members once represented by Solidarity. At the same time, should the price increases be delayed and revised, Polish authorities want to avoid giving the impression of having surrendered to Solidarity's demands.

Police in Gdansk broke up a meeting last week attended by Walesa and a small group of others reportedly discussing protest actions. Three leading Solidarity activists -- Bogdan Lis, Adam Michnik and Wladyslaw Frasyniuk -- were arrested afterward on a preliminary charge of causing public unrest by organizing an illegal action.

For the authorities, who pay huge sums in food subsidies annually to keep prices artificially low, raising prices is a central element of an economic reform program. But the government is having difficulty establishing that program.

Behind the unionists' objections is the awareness that the government's 1985 economic plan foresees no increase in real wages over last year's levels and little on which to hang hopes that belt-tightening this year would produce benefits in the long run.

"It is an improvement of management -- and not price increases -- that should be the main instrument of restoring market equilibrium," a statement by the national council of trade unions said. The union leaders added that the government's price plan would have only a "short-lived effect," doing little to "exert a lasting influence on rationalization of the economy."

They labeled a package of income compensations that the authorities have outlined to cushion the impact of the price increases "misleading and unreliable." They also objected to other plans to push up the cost of electricity, gas and coal, on top of jumps of 100 percent or more for housing rents that were put into effect this year.