President Reagan's top trade negotiator, William E. Brock, says he hopes that the new long-term United States-Soviet grain agreement ''will be one step that will help to restore a more natural, normal relationship between these two major powers.''
''There does have to be a time when you try to move back toward a more normal relationship in a lot of different areas, and this is one,'' Mr. Brock said in an interview.
He finds both superpowers ''sincere about trying to take limited steps to improve things'' and holds out the hope of further moves to ''improve business relations, political relations, diplomatic relations across the board.''
But, says Brock, ''relationships are a two-way street. We simply cannot have continued actions to deprive people of their rights in Poland or in Central America, without it affecting other parts of the relationship.''
Still under discussion, he says, is a proposal by some Reagan administration officials to allow American companies to export at least some types of oil, gas, and pipeline equipment to the Soviets. ''I personally feel that we probably could do additional business in some of these areas.''
He confirmed that ''some figures'' in the administration - reportedly Secretary of State George P. Shultz and Commerce Secretary Malcolm Baldrige - favor at least partial relaxation of US curbs on the sale of oil and gas technology.
Two hard-liners in the administration, Defense Secretary Caspar W. Weinberger and national security adviser William P. Clark, are said to oppose such relaxation.
What emerges is the picture of an administration groping toward less turbulent coexistence with the Soviet regime led by Yuri Andropov, but roiled by crosscurrents of disagreement on how best to proceed.
On the one hand, Mr. Reagan's own anticommunist rhetoric remains harsh, especially where Soviet and Cuban influence in Central America is concerned. In this he is supported by Mr. Weinberger and Mr. Clark.
But the President allowed his trade negotiators to conclude a new long-term grain agreement with the Soviet Union, after refusing for two years to permit such an accord.
The move toward expanded trade arrangements, Brock says, came after the Reagan administration had taken ''political action'' to ''express our feelings about Afghanistan and about the problem of human rights in Poland.''
These actions, he says, ''had had their effect,'' leading to a climate for negotiations on other subjects.
''I think that the Soviets are beginning to realize that President Reagan means what he says and that he does keep his word,'' Brock says.
From this realization, he adds, comes the opportunity for ''an alternative'' to bitter rhetoric, in the form of ''a healthier, more productive relationship, '' leading to better ways of doing business.
To buttress the image of Reagan as a man who keeps his word and of the reliability of the US as a grain supplier, the White House dropped from the grain accord an escape clause that would have allowed Washington to suspend deliveries under certain conditions.
The new agreement, which takes effect Oct. 1, commits Moscow to buy 9 million tons of wheat, corn, and other feed grains yearly for five years, with permission to buy an additional 3 million tons each year. This is 50 percent more than Moscow had been obliged to take under an earlier five-year pact.
Will the new agreement expand the US share of the Soviet grain import market? ''Not necessarily,'' says Brock. ''It is possible, but the Soviets have done what I think any rational person would do and that is to diversify their sources of supply. They've looked to Argentina, Canada, Australia, and to Europe.
''I don't find any fault with that. Countries have to operate in their own best interests. We have to earn an assured market with a better product at a better price. We intend to do that over a period of time.''
Before the partial grain embargo imposed against the Soviets in 1980 by President Carter, the US provided 70 percent of all grain imported by Moscow. The American share has dropped to 30 percent.
What about the usefulness of trade sanctions as a diplomatic tool? ''I'm not a great believer in embargoes. I think that, in particular, the agricultural embargoes of the 1970s did more damage to us than to anybody else.
''I think there is a difference, though, between that kind of (agricultural) option and a strategic option that affects really highly sophisticated equipment that can be used in a military fashion to threaten us or our friends in Europe.''