Vienna — The storm of words between Moscow and Washington is being tested by a practical weather vane this week: grain sales.
The Soviets, despite a fourth bad harvest in a row, are believed to be playing it cool in talks with American officials over the next grain sale. And the tough-talking Reagan administration appears ready to bargain just before the Nov. 2 congressional elections.
''The Russians are good traders,'' an East-bloc trade expert said. ''They will always give something if they are getting something in return. At present they don't see it that way with the US.''
The talks in Vienna began with the Reagan administration eager to please American farmers, who face depressed grain prices following record harvests.
The Soviets, however, have been holding their cards very close to their chests since President Reagan announced Oct. 15 that the US is ready to sell them 15 million tons of grain more than the 6 to 8 million tons provided for by a six-year-old agreement.
And considerable interest has been aroused by Soviet President Leonid Brezhnev's statement Oct. 27 that ''a great deal of work is being done in agriculture in order to eliminate future need for grain imports and fully to meet our grain requirement.''
It is seen as a calculated further endeavor to spur the food program announced in May with a declared aim of shaking out the inherent inefficiencies in Soviet agriculture and making the country self-sufficient in food by the end of the '80s.
At the opening of the talks, delegations met at the Soviet foreign trade mission's headquarters in Vienna. Seeley Lodwick, undersecretary for international affairs and commodity programs in the US Department of Agriculture , said the talks would be ''businesslike.'' The Soviet deputy minister of agriculture, Boris Gordeev, said nothing at all.
Washington apparently is counting on a strong bargaining position (1) because the Soviets, it is claimed, have no alternative to big imports of grain to make up for grave deficiencies in this year's harvest, and (2) because other possible suppliers - notably Australia, Canada, and Argentina - are less attractive or might be less dependable markets for a variety of reasons just now.
But the reactions from Moscow have not been encouraging.
The only public one so far has been indirect, in President Brezhnev's declaration Wednesday that the Soviet Union is out to shed its dependence on foreign grain. He said dependence on anyone, but the implication clearly was to the United States.
His call for self-sufficiency sounded rather like President Reagan's statements to his Western allies that by helping the construction of the Siberian gas pipeline, they will become too dependent on a Soviet fuel source.
To the West Europeans that is a dubious argument, as this American wooing of the Soviets over grain would suggest. The US willingness to sell grain to the Soviets, says one European official, ''smacks of an American dependence on the Soviet market in agriculture.''
The size of the Soviet need as seen by the Americans is also under question. This is underlined by the somewhat modified picture of this year's Soviet harvest.
It has been the subject of dire prediction in the US, but the latest evidence suggests that, whatever the deficiences, it is not not quite all that bad after all.
Reliable Western reports suggest the results in areas harvested in the fall are generally better, changing the picture to some extent overall even as anticipated by the Soviets themselves.
The general impression now is that US estimates of a Soviet harvest this year of no more than 170 million tons were too low, and the consequent expectation of the import need rated too high accordingly.
There may be a certain tit for tat in the Soviet hesitation because of the Carter embargo on sales after Soviet intervention in Afghanistan, though President Reagan has since lifted it despite martial law in Poland since December.
The main Soviet idea, however, is said to be the determination to spread its options and make any future grain imports a ''mix.'' That means American farmers are likely to be in increasing competition with those of Argentina - who supplied three-quarters of Soviet imports in 1981 (though less so far this year) - Australia, Canada, and so on.
Only this week France did a further deal with Moscow for another 450,000 tons of wheat by the end of the year, bringing Soviet purchases of French wheat in 1982 to more than a million tons.