President-elect Ronald Reagan's campaign pledge to end the partial grain embargo against the Soviet Union won't be redeemed without a careful evaluation.

Before his election last Tuesday, Reagan said that the partial embargo imposed by President Carter last Jan. 4 in retaliation for the Soviet invasion of Afghanistan "should be ended" because it "has hurt farmers and has complished little or nothing."

But U.S. grain exports have been running at record levels this year despite the embargo, and some U.S. analysts now say that the partial embargo will have a severe impact on Soviet meat supplies and livestock inventories over the next 12 months.

Reagan advisers say a careful study of the Russian food situation, world grain supplies and political factors would be in line with Reagan's professed desire to acquaint himself with the facts rather than hastily redeem promises made in the heat of the campaign.

The aides decline to be drawn into predictions about what the president-elect will do, and they say there is no indication that he has backed away from his position. But they also deny that the president-elect ever promised any "unilateral concessions," and they acknowledge that a number of specific developments in the world grain evaluation.

These include a major speech by President Leonid I. Brezhnev admitting that the Soviet Union is facing a severe agricultural crisis, a new long-term American grain agreement with China that will take up some of the slack caused by reduced exports to the Russians, tightening world grain supplies, a poor harvest in Argentina and political developments in Poland related to food problems.

Rep. Peter A. Peyser (D-N.Y.), who has opposed efforts in the House to cut off funds for maintaining the embargo, has called on Reagan to "back off." Peyser said that lifing the partial embargo now would send a message of weakness to the Soviet Union.

Noting that the Carter administration also responded to the invasion of Afghanistan with a bill to require 18-year-olds to register for the draft, Peyser said lifting the grain embargo would "send a message to the young people of this country that while Uncle Sam is ready to send them to war to deter Soviet aggression, all is forgiven if the bucks are there."

The Department of Agriculture's director of economics, Howard W. Hjort, says "the Soviets are in deep trouble agriculturally." Hjort, said that rhetoric suggesting otherwise, put out by Repulbican politicians and by spokemen for the grain industry, had been "terrible -- almost a disgrace."

Initial U.S. estimates suggesting that the Soviet Union would harvest about 215 million tons of grains this year have been pared to around 180 million tons as a result of extemely wet weather, flooding and a lack of sunshine in Soviet grain-growing regions. Thus, for the second year in a row the Soviet Union will have had a disappointing harvest. Meanwhile, politically troubled Poland has harvested only 19 million tons this year -- a 10 percent drop from its records of two years ago.

Argentina, which helped the Soviet Union over the last few months with unusually large exports, recently reported a poor harvest and placed limits on exports.

Grain has been enmeshed in Soivet-American politics since 1963, when President Kennedy and his successor, President Johnson, authorized the first large sales to the Russians. In 1972, access to American grain supplies was one of the inducements held out to the Russians by the Nixon administration in the unfolding diplomacy of detente.

In 1976, the Ford administration signed a five-year agreement with the Soviet Union authorizing the Russians to buy a minimum of 8 million tons of grain a year. Agricultural analysts say that the expiration of this agreement in September 1981 could provide the Reagan administration with levelage in any future negotiations with the Soviets over global issues, especially if the Soviet food situation continues to deteriorate. The Soviet Union already has indicated it will buy the maximum 8 million tons allowed in the final year of the agreement.

Reagan said at his news conference in California last Thursday that he believed in "linkage" -- in connecting American concessions to the Soviet Union with Soviet concessions in other areas of interest to the United States.

Peyser said recently that he believed Soviet concern over further loss of access to grain markets may have helped deter Soviet intervention during the Polish labor unrest last summer.

Although grain prices in the United States declined sharply after the embargo was first announced, they have climbed steadily over the last few months, partly because of a severe drought that affected the corn crop but did less damage to wheat and barley. This may have diminished some of the political pressures for a speedy end to embargo.

A number of analyses of world grain stocks points to shortages and higher prices in 1981 unless harvests are excellent. By mid-1981, world stocks may be some 30 million tons below the levels of mid-1980, when stocks were, in turn, 30 million tons below the levels of mid-1979.

The Soviet Union, these analyses show, was able to use 226 million tons of grain this year, only 2 million tons less than planned, by paying premiums for non-U.S. grain and by using as much as 20 million tons of its own reserves. But as the embargo continues, the Department of Agriculture's Hjort said, the Soviet reserves are bound to dwindle and imports will remain a serious problem. Hjort said there were indications that the Soviets had to slaughter more livestock than they had planned last March through June, while they were waiting for their own grain harvest to come in, and that livestock numbers are still greater than present grain supplies can support.

Since January, grain exporters Canada, Australia and the European and Common Market have cooperated with the United States in not boosting their food shipments to the Soviets to take advantage of the American cutback. However, the French government of President Valery Giscard d'Estaing, which has strong support from farmers, as a way of unloading a big wheat surplus.