When President Carter returns to Washington tomorrow night, he faces the difficult task of finding a way simultaneously to rebuke the Soviet Union for its trials of political dissidents last week while encouraging the Soviets to push to completion a new strategic arms limitation agreement.

According to administration officials, the president is determined on both counts. Sources predict that there will be further anti-Soviet measures, probably in the form of new restrictions on Soviet-American trade, but the same sources report encouragement in the administration over the strategic arms limitation talks (SALT) between Secretary of State Cyrus R. Vance and Soviet Foreign Minister Andrei A. Gromyko in Geneva last week.

"We could be on the verge of a breakthrough on SALT," one official said, adding that the president is also likely to curtail or cancel one or two pending trade deals with the Soviets.

Whatever Carter decides to do, he will be caught in unusual political crosswinds. Though a chorus of conservative and moderate voices on Capitol Hill is calling for a stern response to the perceived insult of last week's Soviet political trials, other conservative and influential elements are anxious to preserve basic elements of detente, particularly in the economic sphere. Large multinational corporations and the powerful farm lobby want to preserve if not enhance Soviet-American trade relations.

And many of the same voices that call for some harsh action say they do not want to abandon Soviet-American arms control negotiations, but do seek to make the Soviets pay some price for their treatment of dissidents who the president had personally defended.

The potentially contradictory impulses evident in these calls were embodied in comments by Sen. Bob Dole (R-Kan.), who came out for suspension of the SALT talks, and then said in response to a question from a reporter that he proposed suspending them for 30 days. Would he also favor suspending the billion-dollar-a-year grain trade with the Soviets, so lucrative for many of his Kansas constituents? Yes, Dole said, he would also favor suspending the grain trade - also for 30 days.

An idea proposed by Sen. Henry M. Jackson (D-Wash.) and endorsed by several other senators was to cancel administration approval for a $144 million deal negotiated by Dresser Industries of Dallas, Tex., to sell the Soviets a modern plant to make sophisticated bits for oil well drills.

That deal could amount to nearly half the dollar volume of Soviet-American nonagricultural trade this year. A private businessman involved in the promotion of Soviet-American trade, who has no connection with Dresser Industries and asked not to be quoted by name, said cancellation of the deal "would cause a terrible shock to the trade relationship," and "might very well be the final blow" to the superpowers commercial relations, which have been deteriorating in recent years.

This businessman's theory was that the Soviets - already frustrated by the existing political barriers to trade with the United States - would finally give up their earlier visions of extensive purchases of U.S. goods and technology, orignally regarded by both countries as a central objective of the new relationship that became known as detente.

The latest idea in the White House, according to informed sources, is not to cancel the Dresser Industires sale, but to separate the package into its component parts, and approve only a few of them now, holding out the threat that crucial elements in the package would later be withheld.

The package would give the Soviets a modern plant producing drill bits of a quality they cannot now make themselves. According to congressional critics of the sale, the plant would give the Soviet "25 percent of the free world's capacity" to make drills of this type, and would substantially enhance the Soviets' ability to exploit their vast but often remote oil reserves.

Jackson is reliably said to feel that the Soviets should not be allowed to acquire much-needed western technology to fill gaps regardless of their behavior in the political and diplomatic arenas. Sources close to the senator said cancellation of the Dresser deal could and should be the first step toward imposing rational controls on all technology transfers to the Soviets. Such controls could be used to reward or punish Soviet behavior.

American businessmen have traditionally bridled at the suggestion that their commercial transactions should be conditioned on political factors beyond their control. Strong voices in the government have taken up their side of the argument, contending that as a practical matter and as a policy issue it would be undesirable to try fine-tune trade according to changing political conditions.

But the practical issues are only a part of the present debate on trade restrictions. The White House is also getting political pressure from the right, and feels that it must appear forceful in its dealings with the Soviets or lose all hope of winning congressional approval for a SALT agreement next year, according to official sources.

Therefore the administration is considering some action on the Dresser deal, as well as cancellation of the proposed sale of a large Sperry-Univac computer to Tass, the Soviet news agency Jackson also urged Carter to prohibit this transaction, arguing that the computer is muct bigger than others sold to the Soviets, and that Tass could use it to keep track of dissidents, to promote "black propaganda," or for other purposes that have nothing to do with gathering or distributing news.

Spokesmen for Dresser and Sperry Univac argued in interviews that their deals should be allowed to go through.

Ed Luter, senior vice president of Dresser, said the drill-bit plant sale had been approved on May 30 by the government. He said the technology involved could be acquired in "one of several" other countries, so the United States would only lose an export order by canceling the deal.

An electron-beam welder that is part of the package, and which has been specially questioned by critics of the sale, could be acquired in communist East Germany, Luter said. But, some government officials and congressional critics of the sale dispute this contention, and say the U.S. firm has know how and large-scale experience that cannot be matched by foreign firms.

Oil-drilling equipment is not regarded as sensitive by the informal grouping of capitalist countries (NATO nations plus Japan) that have long agreed to consult together before making any high-technology sale to the Soviets. Hence other countries could freely sell such technology to Moscow.

Computers are controlled by all these nations, so the Soviets could not acquire elsewhere a system comparable to the one it wants from Sperry-Univac. A spokesman for Sperry said in an interview that the system the Soviets want to buy is comparable to one already in use by United Press International and other news agencies in foreign countries.

Numerous government officials agreed in conversations last week that the one area in which the United States probably has significant leverage over the Soviets is in grain, though in most years there is surplus grain for sale in several other countries.

But therehave been no loud public cries for cessations of the grain trade, and administration sources privately acknowledge that there are powerful political and practical reasons for leaving it untouched.

A key reason is the existence of the 1975 Soviet-American agreement on grain purchases in which the U.S. guarranteed to sell the Soviets 6 million to 8 million metric tons of grain every year through 1981.

Beyond that, these Soviet sales "absorb our surplus, and it would be painful to give that up," one official said.

Finally, the uproar among farmers in 1975 when President Ford briefly suspended grain sales to the Soviets is a vivid memory in Washington, and few politicians of any ideological persuasion appear interested in inviting a similar protest.

Grain sales in the first three months of this year totaled more than $462 million, and are expected to be well over $1 billion for the year. These sales have been averaging more than $1.1 billion a year since 1975.

If President Carter does decide this week that he should impose some new restriction on trade with the Soviets, it would represent a departure from the policy he described at a press conference on June 26:

"We have never held out the prospect of increased or decreased trade if [the Soviets] did or did not do a certain [thing] that we thought was best."

If he alters that approach now, the change will reflect the extraordinary complexities Carter faces in trying to pursue both his human rights policy and his arms control objectives with the Soviet Union.