The Kremlin's message to workers sinks in

People are scared. That is how a Moscow woman, shopping for herself and her family, explained the sudden shrinkage in midafternoon crowds at her local grocery.

''People are on the job'' - evidently defying a tradition that has seen many workers slip away to shop, either because they prefer this to work or in a bid to outfox the vagaries in supply of consumer goods and services.

The new Soviet leadership's high-profile campaign for tighter ''labor discipline'' seems, at least for now, to be having some practical effect. There are also signs the Kremlin wants to couple its emphasis on discipline with various incentives.

The open question is where the campaign - still embryonic but involving at least some measures sprouted before former President Leonid Brezhnev's passing last November - goes from here; and how effective it will prove in the long run.

''We shouldn't jump to conclusions at this stage,'' remarked a young, low-level official recently. ''But I am personally frightened by some of the workers' interviews they've been showing on TV in the last few weeks. . . . Some of these people are coming close to suggesting: 'If people don't work properly, let's toss them in jail.' ''

Other Muscovites expressed similar concerns - though a senior official interviewed in late December rejected them as exaggerated. A young man remarked that, although he agrees that tighter discipline is essential to the Soviet economy, there is the danger that achieving it may involve encouraging an atmosphere of mistrust and ''denunciation'' in society.

The Kremlin design, reflected in an officially publicized meeting of Moscow workers in late December, is to create general ''intolerance'' toward citizens who ''by their attitude or conduct harm production,'' and particularly toward ''absenteeism, late arrival for work, and unwarranted departure from work.''

Early this year, police inspectors began spot-checks at various Moscow stores. They stopped customers, asking for identification, place of work - and why the shoppers were not at their jobs.

A young Georgian fruit salesman in Moscow's central farm market had time on his hands to answer questions at midmorning Jan. 25. ''Yes, the market has fewer people than usual,'' he said. ''It'll be jammed on the weekend. But during the week it seems everybody's working.''

Indeed, many of the customers seemed to be pensioners.

On another discipline front - high labor turnover in a centrally planned economy that is nagged by labor shortages - a Soviet newspaper has highlighted new legislation tightening controls on ''parasites,'' people who either don't work or switch jobs too often. The steps, which took effect Jan. 1 but had been approved in October by the parliament of the Russian Republic, include establishment of ''educational labor prophylaxis centers'' for people convicted of ''vagrancy, begging, or of leading another form of parasitic life.''

Although the newspaper account Jan. 19 did not go into detail about the new centers, diplomats are assuming they will be something of a cross between existing labor colonies for juveniles and ''therapy prophylaxis centers'' for alcoholics. Soviet officials have not immediately been available for explanatory comment.

There are also reports - not yet officially confirmed - of a recent, unpublished ''administrative measure'' limiting workers to two changes of job per year. This would stop short of legislation in force from 1940 to 1956 barring industrial workers from any change of employment without official approval.

But the question of precisely how these new ''discipline'' measures are to be enforced is at least as important as the particular measures that eventually emerge.

Under Leonid Brezhnev, for instance, laws were tightened against ''under-the-counter'' sales - that is, for bribes - of consumer goods in short supply. But this seemed to have no major effect.

Interestingly, when Georgian authorities polled ''speculators'' serving sentences for black-market peddling, about one-fourth of the most blatant speculators did not ''consider speculation a crime,'' according to a 1982 Soviet newspaper report.

Fifteen percent saw it as an ''ordinary business transaction,'' and 17 percent ''regarded it as a service in which scarce goods are supplied for appropriate payment. Only 7.2 percent said their friends took a negative view of their speculative dealings.'' About 20 percent told the official interviewer they would go back to speculating once their sentences were over.

Under Joseph Stalin, a few absences from work theoretically could send an offender to a labor camp. Dissident historian Roy Medvedev notes, however, that this was not always stringently enforced.

An economic manager who feared losing a worker he would have trouble replacing ''would think twice about reacting too sharply to occasional absences, '' Mr. Medvedev explains.

Stalin's successors have launched intermittent campaigns against economic inefficiency, indiscipline, or corruption, but these have been diluted by officials, such as farm and factory managers, who were supposed to carry out the policy.

This has been especially true as labor shortages have become more keenly felt in recent years.

A Soviet journalist's account of a Latvian collective farm suggests managers are leery of dismissing even drunken workers. He has dubbed them ''irreplaceable'' alcoholics.

The senior Soviet official who, during an interview last December rejected the prospect that the new leadership would get to the point of ''jailing'' indisciplined workers, did remark that only a truly nationwide tightening of discipline could succeed in getting at the core of problems like absenteeism, high labor turnover, or on-the-job drinking.

The new leadership's early hope, officials suggest, has been mainly to communicate a new seriousness of purpose in applying legal and administrative sanctions already on record - for instance, the official news media suggest, holding party, government, factory, and farm officials personally accountable for their underlings' violations of existing discipline codes.

At the same time Mr. Andropov, the new Communist Party leader, has stressed the need for wider use of ''incentives'' for workers who work well.

Even this carrot in the official strategy could prove tricky to apply. As a Soviet newspaper pointed out Jan. 23, the effect of monetary incentives can be diluted by a lack of consumer goods for increased cash to chase.

Meanwhile, the new leadership does seem to be making a concerted effort to provide increased stocks of some prized foodstuffs.

Shops in Moscow and, travelers say, in various other parts of the country have been especially well stocked in recent weeks - with imported citrus fruits, for instance, or sausage.

The government has also announced what seems a flip side of the police checks on workday shoppers. A recently published decree suggested that various shops and other service outlets will, by the end of March, open later in the morning and stay open later at night to better serve customers who work during the day.

Even with the ''discipline'' campaign of recent weeks, not all Soviet workers have abandoned midday absences.

The other day a Moscow office worker broke an afternoon date made weeks earlier:

''I used to take much of my work home with me, but I've stopped doing this as much,'' he explained.

Then he added: ''As it happens, the reason I can't make the date this afternoon is that I'll be busy with a friend in the middle of the afternoon, getting his car repaired.'' Such repairs are a daunting feat for Muscovites to accomplish after work hours.