The Soviet Union has made a significant conciliatory gesture toward President Reagan by unexpectedly agreeing to a new pact that provides for higher Soviet purchases of U.S. grain over the next five years.

This was the prevailing view among foreign and Soviet sources here, who interpreted yesterday's agreement as reflecting Kremlin hopes that expanded trade would have a positive impact on political relations between the two superpowers.

It has been speculated here that Moscow was tempted to use the grain trade as leverage on Reagan, who has been viewed here as being under pressure from financially stricken American farmers to regain access to the lucrative Soviet market. In the current year, the Soviets have purchased only 6.2 million tons, or the minimum amount they were committed to buy under the existing agreement.

Under agreement, the Soviet Union will have to buy at least 9 million tons annually and could purchase up to 12 million without any additional negotiations.

Moscow thus app have renounced the means of stirring political trouble for Reagan in the farm belt during the 1984 election campaign, calculating that he i run again and may win another term.

The Soviet action also provides the president with an opportunity to tell the farmers that he not ona partial grain embargo imposed by his predecessor but increased the guaranteed purchase levels by 50 percent.seen as significant since the Soviets have developed alternative grain markets during the past few years and eed grain crop of their own this year. Western diplomats said Moscow now expects a "positive response from Washd lead to a restoration of more normal relations.

Some observers saw the accord as a straw in the wind and ntext of these recent developments: a compromise at the Madrid talks on European security and cooperation, Poland's lift of martial law and Moscow's reported undertaking to free some jailed Soviet dissidents this year.

There wa western and Soviet sources today that these developments may create a climate in which a Reagan-Andropov meeting could become possible, although it wssed that the two men would require beforehand something concrete to agree upon.

Some western observers said the Soviets now appear more willing to give Reagn the political benefits of a summit in a presidential election year should he be willing to give them somethie key issue, however, rests on the resolution of divisions at the Geneva talks on medium-range missiles in Europe.

Moscow's decision to enter into a new long-term graireement is seen as having been motivated by other factors as well. By expanding its imports of U.S. grain, Mosan in a position from which he could find it difficult to urge U.S. allies to curb exports to the Soviet Union Soviet leadership is seeking to stabilize trade relations with the West.

While this country expects a goodar, it may be forced to return to massive food purchases abroad in the future.

The Soviet media has not pubut the new agreement, and it is not clear whether the Reagan administration pledged to forgo future economic elier had insisted on such a pledge, arguing that the United States is an "unreliable" trading partner and that it was using food sales as a weapon of foreign policy.

In 1980, president Carter canceled contracts for 17 million tons of grain in retaliation for the Soviet invasion of Afghanistan. The embargo did not affect the minimum 6 million tons annually.

While Reagan lifted the embargo in 1981, he used export controls in an aborfort to block or delay the construction of the gas pipeline from Siberia to Western Europe. He also imposed a ban on negotiations for a new long-term agreement on grain sales out of concern for the political situation in Poland last year.