MOSCOW, SEPT. 4 -- The angry shoppers of Moscow have suffered the ultimate indignity: Even bread has disappeared from the shelves. There is little mystery anymore why Mikhail Gorbachev is now only the eighth-most popular politician in the capital.

"Now the one thing we could always depend on has suddenly disappeared," said Marina Simyonova, storming out of a bakery near the Ukraine Hotel. "This fills your soul with tension, with anger. Is this what all our great reforms are about? If this is perestroika, I've had about enough."

Despite a record Soviet grain harvest, the bakeries of Moscow are suddenly filled with little more than a stream of furious men, women and children in futile search of their daily loaf. There have not been such shortages for nearly 30 years.

Lenin founded the Soviet state in 1917 under the revolutionary banner of "Peace, Land, Bread." Peace turned into civil war, and land went into the hands of the state, but the availability of bread, fresh and subsidized, became a propaganda symbol of the Bolshevik victory. So powerful is the Soviet cult of bread that until recently there was a Bread Museum on one of Moscow's main boulevards.

Today, Gorbachev sent a telegram to regional leaders ordering them to guarantee that farmers deliver grain to state contractors. "Many state and collective farmers are unjustifiably curtailing sales to the state, violating contract discipline," it said.

As the old centralized economy collapses and a market economy awaits its difficult birth, shortages have become the center of everyday life. Milk, meat, medicines, vegetables, cheese, candy, vodka, poultry, baby food are nearly impossible to get. Schoolchildren were unable to find notebooks for the start of the school term Monday. The most common curse of the Soviet shopper is the alliterative, double negative neechivo nyet -- "no nothing."

To stand by the door of Bread Store No. 150 on Kutuzovsky Prospekt for an hour this afternoon was to sense the pure frustration, the fury of the Soviet citizen who reads newspapers filled with high-minded speeches of the Gorbachev government in the morning and then sets out like a prehistoric hunter-gatherer to find some food for the family.

"This is getting so humiliating that I wouldn't be suprised to see rebellions and food riots someday soon," said Galina Sokol as she left the store with one green onion.

At a congress of the Russian republic's Communist Party here today, Politburo member Yuri Prokofiev declared that the worse the shortages get, the faster Gorbachev risks losing his power and his program of reform.

"The tangible danger has arrived when democratization may become a mere episode in the history of the country as it moves on a path from the old command-administrative system to chaos and disorder and, finally, dictatorship," Prokofiev said.

The summer has already witnessed the phenomenon of "tobacco rebellions" in Moscow and Leningrad. Until the government bought millions of cigarettes from Bulgaria last week, angry smokers would stop traffic and break windows to show their displeasure. Now there are cigarettes in the kiosks, but prices have quadrupled.

Bread is an even more explosive subject in the popular consciousness. In June, when Prime Minister Nikolai Ryzhkov proposed that as part of an economic reform plan the government triple the price of bread, people panicked, flooding the stores and buying up every available loaf. The Soviet legislature quickly blocked the program, and Gorbachev is now putting the last touches on yet another economic reform package -- with no rise in bread prices. The new program is said to be based largely on a plan sponsored by Boris Yeltsin, president of the Russian republic and the country's most popular politician.

Bread is such a symbol of Russianness that last year, fresh black bread from Moscow was flown to New York daily and sold at Bloomingdale's for $4.50 a loaf. The price here is 18 kopecks (about 30 cents).

There are plenty of explanations for the sudden bread shortages -- as well as reassurances from officials that there will soon be loaves in the stores.

Soviet television reported that more than 30 of the area's bread factories are working "abnormally" and blamed the low production on dilapidated machinery and transport. The capital's bread factories and bakeries have an average age of 100 years, and perhaps the only modern baking facility in the metropolitan area is the new bun plant just built by McDonald's to service its Moscow restaurant.

Other press reports blamed a labor shortage for the lack of bread, saying that many bakers have left state factories to seek higher-paying jobs in new private businesses. Mikhail Chaplin, head of Moscow's bread ministry, blamed the difficulty on the fact that "our production basis is at about where it was in the 1950s, when there were not quite half as many people in the city."

Meanwhile, Moscow Mayor Gavril Popov, who took to the radio last week to instruct listeners on how to roll their own cigarettes, now has proposed that hundreds of soldiers be sent to bread factories to help increase production.

"Who is in charge here?" asked Sergei Bershin as he left Bread Store 150 empty-handed. "Isn't anyone in charge?"