BLONIE, POLAND, JULY 11 -- Roman Mosinski, a burly Polish farmer who grows corn but cannot live on the price his new non-communist government pays him for it, parked his tractor right in the middle of the main highway that connects Warsaw and Berlin.

In doing so, he joined thousands of other angry farmers today in the boldest challenge so far to a government that is finding it harder and harder to persuade Poles that economic sacrifice is an essential condition of free-market reform.

The farmers used their tractors, their wagons and even their animals to block nearly every major highway in Poland for two hours to dramatize their demand for guaranteed prices that will cover the exploding costs of fuel, farm machinery and fertilizer.

Since the first of the year, farmers have been squeezed between high interest rates for loans and the failure of bankrupt government cooperatives to pay for delivered farm produce. In addition, consumer demand has fallen sharply as many Poles -- responding to the loss of government subsidies and rising food prices -- cut back on buying groceries.

Here along the Warsaw-Berlin highway, Mosinski scrunched up his round, weathered face in contempt when asked to assess arguments by the Solidarity-led government that guaranteed farm prices would cripple an effort to make market forces, rather than bureaucratic decree, the guiding principle in rebuilding the country's shattered economy.

Neither could he accept the government's claim that special benefits given to one group of workers would be at the expense of all others, and the nine-month-old government's plea for "patience" struck him as insulting.

"Patience! You can't eat patience for breakfast or for dinner. You can only eat bread," said Mosinski.

Just down the road, Gabriel Janowski, chairman of Rural Solidarity, the farmers' alliance that organized the blockade, said today's "drastic measure . . .was just proof of how deep the farmers' problems are."

"This protest must bring results," said Janowski. "We can't have war between Poland and farmers."

In recent weeks, farmer protests, including occupation of the Ministry of Agriculture in Warsaw, have forced the government of Prime Minister Tadeusz Mazowiecki to admit that farm policy has been "sluggish."

Last weekend, Mazowiecki fired the minister of agriculture, arranged concessions on low-interest loans and promised to restructure the state agency that buys food from farming communities. However, sticking to the principles of a his "shock therapy" economic reform program, Mazowiecki vowed not to give in to the farmers' demands for guaranteed prices.

"We will not talk under coercion," government press spokesman Malgorzata Niezabitowska said on Polish television last night. "We deplore the farmers' resorting to methods conflicting with the law, such as blockading roads and occupying state buildings."

Last month, the government used police to clear a roadblock and remove farmers from the Ministry of Agriculture. Today, police at the roadblocks took a more conciliatory line. They said their instructions were to maintain order and advise motorists of alternate routes.

After sitting for two hours in a mile-long queue on the Warsaw-Berlin highway, one grumpy motorist complained that farmers are refusing to face up to the realities of a free-market economy.

"It is pointless to protect many of these small farms. Their production costs are too high. You have to have a free market, and certain farms have to vanish. Only the biggest should survive," said Piotr Wiebicki, a 36-year-old Polish playwright, who lives and works in West Berlin.

Farms in Poland are among the smallest and least mechanized in Europe. One in every eight citizens here is a farmer. The ratio in West Germany is 1 to 45, in Great Britain, 1 to 100 and in the United States, 1 to 76.

Although the government has not said so publicly in recent weeks, its senior economists have argued that the bankruptcy of many thousands of the country's 2.5 million farmers is a necessary part of Poland's economic reform process.

None of this washes with Mosinski and his friends. For a decade, they were anti-Communist supporters of the Solidarity labor union movement and its agricultural ally, Rural Solidarity. It has been a source of pride among Polish farmers that their sector of the economy managed to retain its character and traditions despite four decades of Communist rule.

According to the men at the roadblocks, the supposed savior of individual freedom -- an elected government -- is making life harder than ever for farmers, and they feel betrayed.

Mosinski said he heard from a Solidarity leader at the beginning of the year that participation in the free market would raise the price of corn to world market levels, around $140 to $150 a ton, but the harvest price this summer is only about $6 a ton

Mosinski said that he is willing to bring his tractor out to the highway as many times as necessary to demonstrate to the government that it has not lived up to his expectations. "We want to express our dissatisfaction," he said. "This is the only method we have."