Never in the past decade has the prospect of widespread shortages of fresh meat and dairy products so darkened the horizon for Soviet consumers as this spring, when the American grain embargo looms in the minds of millions.

A mood of frustration and disappointment sours the pungent atmosphere of this capital's markets as buyers with rueful, tight-lipped looks contemplate empty shelves or astronomical prices they are sure are only a harbringer of worse to come.

In the well-stocked markets where farmers put their private goods on sale, $21 buys a chicken weighing three pounds, $5 a pound of stew beef and $3 a pound of veal. This in a country where the working person's average income is the ruble equivalent of $270 a month.

In the sparsely supplied state stores, where prices are much lower, milk and such indispensible ingredients of the local cuisine as sour cream, cottage cheese and yogurt frequently are not available. Even official figures admit a 4 percent decline in dairy production for the first two months of 1980 compared with 1979, a result of continuing major problems with fodder supplies for the dairy herds.

The Soviets have secured elsewhere all but a few million tons of the 17 million tons of feed grain embargoed by President Carter in retaliation for the December invasion of Afghanistan. But the delays and overall shortfall in foreign grain purchases will further disrupt dairy production in May and June Western diplomatic sources here say.

On the street, angered consumers readily blame their plight on the Americans.

"They are trying to starve the herds," said one woman, echoing the official explanation for the shortages. But many also lay the blame for the difficulties on their own leadership in a combination of anger and pride. As one man put it, after describing endless shortages of meat in his home near the Black Sea in Sukhumi, "We're feeding half the damn fraternal socialist world, from Cuba to Kampuchea [Cambodia] and now Afghanistan."

The Soviets, who have never publicly disclosed here that they were heavy purchasers of U.S. grain, have said relatively little about the embargo of 17 million tons of feed, which they originally sought to fill the gap left by a terrible harvest last year.

According to well-informed Western sources here, the Soviet Union has made up all but 5.5 million tons of the 36 million tons of grain it planned to import through June 30. This amount includes 8 million tons already purchased from the United States under the existing grain trade agreement that expires next year.

The Soviet purchases have raised world grain prices. Specialists here note that the Soviets "are out offering attractive prices" of as much as $25 per ton more for corn from Argentina than American corn, at $179 per ton, was fetching just last month. They have all the hard currency they need for this from sale to Western countries of oil and precious minerals.

Because of delays in arranging shipping for this foreign grain, experts here anticipate that the Soviets will not be able to ride out the year without reducing their livestock herds in distress slaughters. Official Soviet figures show that this has already started.

The weekly Economic Gazette reported two weeks ago that beef production rose 13 percent in the first two months of this year as compared to 1979, while pork was up 10 percent and poultry 16 percent. Part of this increase, however, can be attributed to an extremely cold winter last year, which disrupted both agriculture and transportation and led to a lower than average slaughter.

One of the many continuing mysteries in this country is where all this "extra" meat goes. It has not yet appeared here in Moscow, which stands first in the official supply line. And in hundreds of regional cities, such as Sochi, Novosibirsk and Ryazan, Soviets say that fresh meat at reasonable prices has been a 10-year rarity despite official figures that show continuing advances in total per capita meat production.

Whenever the influx of extra meat arrives at the market, Soviets still are looking beyond to succeeding new months of scarcity. Chronic shortages are a fundamental reality of Soviet life, and while people may grumble, if there is no meat they will simply eat fat, such as salted pork fat at $3 a pound.

Western observers do not expect mass protests, such as swept Poland twice in the past decade and helped influence Soviet President Leonid Brezhnev to launch the costly drive to improve Soviet meat supplies.

Meanwhile, Western experts estimate that the 1980 grain harvest may total about 220 million tons, far below the goal of 235 million tons in the five-year plan, yet adequate to preserve the livestock herds without disastrous reductions or massive foreign grain purchases. However, the caution that spring is about two weeks late in some northern parts of the vast Soviet grain belt, which could cause harvest setbacks impossible to predict.

One of the consequences of the Carter embrgo has been that talks to exchange crop survey teams between the two nations are suspended and it is unknown when or whether an American team will be able to make the detailed inspections considered necessary for accurate harvest prediction.