Moscow — Bolstered by the prospect of its first good grain harvest in five years, the Soviet Union has been playing it tough in negotiations with the United States to renew their expiring grain pact.
At the third round of talks in Vienna this week, the team headed by Deputy Trade Minister Boris Gordeyev was reported to be standing firm on its refusal to accept US demands for a substantial increase in minimum Soviet purchase levels.
Under the present agreement, which runs out at the end of September, Moscow must buy a minimum of 6 million tons of US grain a year, half of it wheat and half corn. Under pressure from Midwestern farmers, the administration is trying to raise that level to 8 million or more.
With world grain stocks far exceeding demand, the Soviets know they are in a buyers' market and can play for time. They underlined their attitude by turning down flat an Argentine request last week to increase the floor level for supplies from Buenos Aires from the present 4.5 million tons a year.
But market conditions aside, Moscow's trump card is the state of the 1983 crop.
According to current forecasts from the US Department of Agriculture, the Soviet harvest this year should total 200 million tons. Some Western farm experts in Moscow believe it will be even higher. This means the crop is on course for the best result since a record 237 million tons in 1978.
The intervening years have seen a succession of failures, with results so embarrassing for the Kremlin that it halted publication of all harvest statistics two years ago. According to Soviet sources, the 1981 yield was only 150 million tons and last year's was less than 180 million.
Even if a 200-million-ton crop will look good in comparison with those figures, it will still be far below the government's official target of 238 million tons in 1983. But it will mean Moscow can cut back substantially on imports from outside producers like the US, Argentina, Canada, and Australia.
Two years ago the Soviets bought a record 46 million tons. Forecasts for this year suggest import levels will be below 30 million.
Western farm experts say the improvement in the 1983 crop is due almost entirely to weather conditions, as ample rainfall alternated with hot sunny days during the crucial growing period of the spring plantings.
The Soviet press has not disputed this view and makes clear the kinds of problems that dogged past harvests have not been resolved. These include severe fertilizer shortages, poor quality seeds, unreliable harvesting machinery, and a dire lack of adequate storage space for the cut crop.
The Kremlin leadership under President Yuri Andropov has declared its firm determination to sort out the ramshackle farm system, and over the past few months it has been cautiously introducing reforms in agricultural administration and the way the work is done in the barns and fields.
The most important of these is the introduction of the so-called ''team contract'' system. This allows groups of workers to set themselves up on a semi-independent basis and subcontract work from the farm management. The members of the team share out the profits among themselves but have only a small guaranteed wage to fall back on if they mess things up. Surveys have shown that where they operate, labor productivity can rise by 30 to 40 percent.
Although the leadership is backing the system, there is stout resistance from bureaucrats and farm managers, who apparently fear dilution of their powers, and often from the workers themselves. With little tradition of private initiative, many say they prefer the security of a set wage to the uncertainty of a bonus that could be wiped out by a bad crop.
The Western agricultural experts say the new methods have not been implemented widely enough to have much effect on this year's harvest. But they could be a major factor in determining whether the poor performance down on the state farms will start to pick up from next year.
Mr. Gordeyev and his team in Vienna are also unlikely to be placing too much faith in a sharp improvement in the coming years.
Soviet trade officials say privately Moscow is keen to renew the grain pact with Washington because it means solid guarantees, especially for supplies of wheat that are not always available at similar prices elsewhere. They make no bones about the fact that Moscow expects to have to import sizable quantities of grain for several years to come.