All though the summer, the official Soviet press warned of indifferent harvest results, and now the subject has narrowed in the minds of many in this capital to just one hot topic: the potato.

Zooming prices and shortages have hit this Slavic dietary staple, the dismal result of one of the most unpleasant and unsettling summers in recent times. For every American who may have cursed the sun for the drought it brought this summer, it is likely that there was at least one Soviet citizen who cursed the rain and chill here.

Large sections of western Russia's croplands and pastures were heavily flooded, and the unexpectedly cold weather that miraculously was sunny and hot for the Moscow Olympics turned family garden plots -- the cornerstone of consumer vegetable and fruit supplies in the Soviet Union -- into unyielding patches of rotted plants and vines.

The agricultural paper Selskaya Zhizn warned that the damp has dangerously impeded the potato harvest, while a regional Moscow newspaper hinted that a potato shortage is probable.

One unhappy babushka, or peasant lady in a sidewalk conversation the other day detailed how her entire garden of cash crops -- potatoes , tomatoes, cucumbers and onions -- had "rotted in the ground or never did anything" because of the cold and damp.

Some Western correspondents here have reported potato hoardin and long lines of shoppers queuing up for what in the past has seldom been missing from Moscow's shelves andstores. A tour of several private farmers' markets last week showed that prices have jumped approximately 30 percent, to 60 kopecks (about $1) per kilo (2.2 pounds) from last year's price of 40 kopecks per kilo. The line at the central market next to the Old Circus in Moscow numbered about 20 at midmorning, and few seemed happy.

"They say the price is 60 kopecks," one elderly woman groused, "but they'll charge anything they can get and they get it." Behind the scales, the whitejacketed peasant woman smiled and turned to the next customer.

A white collar worker fretted: "When there was a shortage of fruit, we got it from the Arabs. And when potatoes were short, we got them from Poland. We can stil get the furit, but now where will we get the potatoes?"

Put the trouble may turn out to be small potatoes compared with other Soviet agricultral problems.

The U.S. Department of Agriculture already has predicted a Soviet grain harvest of no more than 210 million tons -- 25 million tons less than the state target and the second major harvest shortfall in two years. Other Western sources say the total may fall well below the 210 million figure. Western analysts believe Soviet losses resulting from spoilage caused by dampness could approach 20 percent, or double the normal rate.

Moscow has moved into international grain markets to stave off starvation for its carefully built-up livestock herds, and is expected to buy the full eight million tons of U.S. grain available without special authorization under the bilateral grain agreement with Washington that soon enters its last year.

The Soviets are likely to get most of the extra grain they need from Austraila, Agrentina, Canada, Eastern Europe, Britain and Fance. Many analysts believe that the Soviets nearly have made up the shortages caused by President Carter's grain embargo earlier this year in response to the invasion of Afghanistan.

However, recent official Soviet figures for both Soviet meat output and the size of livestock going to slaughter indicate serious problems with the country's carefully nurtured meat herds.

In the face of a steadily increasing population, Soviet state meat production was 5 per cent less for the first seven months of 1980 than for the same period last year. Market hogs are about 8 pounds lighter than the average weight for last year, and beef cattle are about 25 pounds lighter.

There seems no sweetener for this sour picture, which from the Kremlin standpoint could not have occurred at a less appealing time in view of the food strikes in Poland that have brought about fundamental changes in the established order within that country.

In fact, the weather has been especially hard on the Soviet sugar beet crop. Western sources say it will not exceed 84 million tons, 14 million less than the state target and about 6 million less than the average for the past four years, Moscow's usual outside sugar supplier, Cuba, has severe harvest shortages, and the world sugar price has moved upward in recent months in response to these factors.

For the Soviet farmers and their bosses this year, when it rains, it seems to pour.