Vladimir, a journeyman carpenter on his way to a noontime break, smiles. ''There's this joke going around: We know the Americans have a neutron bomb that destroys people but not buildings. Then, there are other nuclear weapons that destroy everything. . . . The question is what kind of bomb we Soviets have developed: It leaves everyone alive with nothing in the shops.''
For the Brezhnev regime, food-supply problems in the Soviet Union are, increasingly, no laughing matter.
Yet as Mr. Brezhnev's Communist Party Central Committee met May 24 to be handed an overall ''food program'' 18 months in the making, there seemed little doubt that any long-term resolution of Soviet food woes would depend on his successors. Even the most ebullient optimists here know there are no easy answers.
In the Western press there have been reports of a confidential study prepared for the top Soviet leadership that suggests a serious decline in the country's ability to feed itself. But few of these problems are secret.
All of them, senior officials suggest, came up in the months of preparatory research and discussion on the Brezhnev food program. Some general policy priorities were said to have been clear from the start: ''rational-izing'' of planting, for instance, to devote more acreage to high-quality feedgrain for livestock; a rejigging of transportation routes; some form of ''incentives'' for farmers to work hard and stay on the farms.
To ''solve'' Soviet food problems is to battle alcoholism, absenteeism, and poor management; to expand and overhaul storage and transport facilities; to get rural folk to make babies and harvest instead of moving to the city; to introduce new machines and keep them running; and to realign a bickering bureaucracy.
Most important - and most difficult - the Kremlin must find a way to get more of its subjects to care. The corrupt must turn conscientious; the lazy, industrious. The selfish or indifferent must somehow be moved by the plans, decrees, and relentless cheerleading of the few who rule.
''The main problem is with people, cadres,'' says a middle-aged scientific researcher on his way to work barely a mile from where the Central Committee ''food plenum'' is convening. ''On the farms, they drink a lot. . . . And even when people work, they know their bosses are apt to keep things for their own profit.''
In a nearby park, a gas-industry inspector savors an interlude between trips to offshore drilling sites. After a few days' chilly hesitation, spring seems to have decided to stay. The young man is feeling upbeat, even about the food situation. ''Here in Moscow, things are OK by and large. It is true that all you have to do is travel 40 kilometers to find nothing. . . . But here, we are OK.''
His tone changes as he talks: ''It is a question of moral consciousness and commitment, this food question. . . . And it is too early (in history) to rely on such qualities here.''
He says - as do some quite senior Soviet officials - that the challenge lies not so much in formulating a ''food program'' as in putting it into practice. ''Somehow, along the line, even good policies get lost. . . . Local officials lack initiative, for one thing.'' Like many other Soviets, he has a small chunk of land in the countryside that he farms privately. Encouraging these ''private plot-holders'' has, for some time, been part of official strategy to offset shortcomings on the collective farms.
''But, take this example: Next to my piece of land is another small one my neighbor says he doesn't want to farm. I asked the head of the nearby collective farm, which also doesn't want to use that land, whether I could go ahead and farm it, too. He said, 'No. Absolutely not. You already have enough land.' So it is going to waste and no one farms it.''
As detailed by Soviet officials, their state news media, and distinctly unofficial Soviets, agricultural problems are extend from farm to shop counter:
* On many collective farms, workers drink a lot, laze a lot, and ship out a lot less grain or livestock than the land might yield. Many workers drift off to the cities. Even counting the cities, birth rates in the European part of the country have been falling.
The labor shortage is especially acute on the farms. In addition, the Soviet press says, there are problems with breakdowns in machinery, supply of spare parts, and management. Fertilizers and pesticides are often in short supply or misused. A recent radio report said potential crop levels were decreased ''30-40 percent, and sometimes even more'' by insects, plant diseases, and weeds.
* Once food leaves the farm, the problems multiply. More than half the nation's grain crop is stored near the farms that grow it. According to a recent Soviet newspaper account, ''Roughly 40 percent of this total is stored in unsatisfactory conditions.''
Substandard roads, a severe shortfall of properly insulated or refrigerated trucks and railroad cars, mechanical breakdowns, and oversight combine to make transportation a delicate business.
In an article April 9, a Soviet agricultural expert said that ''in gathering, transportation, storage, and industrial processing, we lose roughly one-fifth of total grain, vegetable, and fruit crops.''
For potatoes, the figures are higher: up to 25 percent lost in winter storage. A shortage of proper packaging, such as milk containers, means further wastage.
* Then comes the shop counter. Shortages combine with artificially low prices on some items in state shops to provide ample opportunity for storekeepers to make a quick ruble. They do. Selling products ''through the back door'' is a favorite pastime.
Despite all this, no one seems to be starving in this vast nation, as far as Moscow-based foreign correspondents can determine. Even the third poor grain harvest in a row - 158 million tons, or some 80 million below target, according to a Western expert who met recently with Soviet officials - has allowed generally good bread supplies.
People here eat a lot of bread. Outside Moscow meat and milk and butter are much harder to come by. In many areas, ration cards are used to ensure distribution of scarce products, at offices or factories.
''Yes, where I come from we have cards,'' says a slight young woman from Kirov who works in Moscow. ''Butter is by cards. You get 200 to 400 grams a month, through your work place, depending on where you work. . . . Sausage is the same way.'' She says meat is available in the private farmers' market. ''But the prices are too high, so we don't go.''
Officials are predicting the food program will move to untangle an enormous economic- and agricultural-management bureaucracy by bringing nearly a dozen food-related government ministries under a single authority. The official press has suggested that regional authorities will be given greater power.
Again, implementation will be the key. How much power will a new food authority have? Any agricultural overhaul will demand enormous resources. Even before the food-program meeting of the Central Committee, some 7 billion rubles ($10 billion) had been earmarked for improving roads in the current five-year plan.