In a massive job action believed to be without precedent in Soviet history, workers at the Soviet Union's two largest automobile factories struck the plants for three days recently to protest poor food supplies.

According to unofficial sources who cannot be named, more than 200,000 workers may have been involved in wildcat strikes that stopped or slowed down production at the Togliatti auto works and the Gorki auto and truck plant from May 6 to May 8.

The peaceful protests were settled when authorities rushed fresh food and other supplies to the two industrial complexes located in central Russia.

There was no mention of the disturbances in the official Soviet press. A Togliatti city official describd reports about the strike as a "provocative anti-Soviet statement."

But as reconstructed from scattered but credible reports now reaching Moscow, the walkouts began May 6 at Togliatti when some 70,000 assembly line workers joined a sudden strike by city bus drivers who were refusing to do more work without extra pay.

The Togliatti auto workers, 650 miles south of Moscow on the Volga River, produces 700,000 passenger cars per year under the Fiat license or more than half of all Soviet cars.

On May 7, according to these accounts, thousands of workers at the Gorki auto and truck complex located 300 miles north of Togliatti, also on the Volga River, walked out to protest food shortages.

The Togliatti walkout reportedly lasted one day before it was settled peacefully when authorities rushed in food supplies and backed the bus drivers in their despite with the management. But the Gorki walkout lasted two days and involved at least four arrests, the sources said.

Independent verification of these reports could not be obtained. One source confirmed that assembly line workers had created major shortages at Togliatti but could not specify the date of the reason for them.

Strikes are not permitted in the Soviet Union, which is, theoretically, a workers' state.

But food supplies have been unusually short throughout European Russia and Siberia this spring, presumably fueling widespread workers discontent.

Apart from an extra long winter and depleted fodder for dairy herds, the food shortages probably reflected the effects of a grain embargo President Carter imposed following the Soviet invasion of Afghanistan. Also, the authorities are believed to have been stockpiling for the Moscow Summer Olympics so that they could display ample food supplies before thousands of foreign visitors.

The pinch has been sharpest in milk and dairy products, which are about 6 percent below last year's totals. Significantly, the Soviet press denounced severe under-production of these items in the Volga region around the Togliatti complex two weeks after the reported strikes but without mentioning the disturbances.

There is no hint of coordination between the two plants' workforces, though the Togliatti incident may have emboldened the Gorki workers. Sources said workers at that plant, which makes 80,000 Volga sedans and thousands of trucks yearly, have been restless since April over food cutbacks. One source said handwritten pamphlets listing complaints appeared in April, allegedly asserting "We should show who is boss of this factory," but containing no ultimatum.

Some dissident sources consider these reports highly exaggerated and say they could normally expect to hear of such troubles, but had not. Dissident leader Andrei Sakharov was exiled to Gorki last January.

The Togliatti bus drivers are said to have walked out last year as well, when about 200 drivers on Aug. 10 refused to work because of sharp differnce with their management.Buses are the main transport for the workforce which is housed in vast high-rise complexes about 10 miles from the plant. Thousands of workers went on foot to their jobs anyway, it is said, but last month supported the drivers by staying home and pressing their own grievance over food.

The two factories' workers are among the elite of Soviet industry. Motor vehicle production at the Gorki plant was organized along modern lines 50 years ago with the help of Henry Ford. The Togliatti complex was bought outright from Fiat of Italy in the late 1960s, assembled on its present site and named after the longtime Italian Communist Party leader Palmiro Togliatti.

Production began in 1971 of cars called Zhiguli here. Despite their cost of a minimum 6,600 rubles ($10,256), they are relatively plentiful and have brought the Soviet Union into the auto age. Sold abroad as the Lada at cut-rate prices, the cars earn hard currency. Two months ago, the Soviets announced plans to sell Ladas in the United States next year, with a sales goal of 50,000 by 1986.

Job actions by Soviet workers are rare and never officially reported. The most serious strike known in the West occurred in June 1962 at Novocherkassk in southern Russia when locomotive and textile workers struck protesting food price hikes. Nikita Khruschev ordered in troops and hundreds may have been killed. In the Brezhnev era, informed sources say, official policy has been to meet worker demands "because they are usually justified on economic grounds and never political."

However, a free trade union movement which began here in 1978 under the leadership of miner Vladimir Klebanov has been suppressed. Klebanov was arrested and is now confied to a Soviet criminal psychiatric institute.