The Polish crisis already seems to be hurting the Soviet economy, an enormous machine that churns out lots of natural gas, oil, hard-currency earnings, inefficiency, corruption, and food shortages.
And now the new US economic sanctions may well compound that strain - although public Soviet reaction will surely deny this.
At first sight, the Reagan package appeared less far-reaching than the Soviets might have feared. It does not include any cutoff of arms control talks nor does it impose a flat grain embargo - both contained in the Carter sanctions after the Soviet invasion of Afghanistan.
In addition, the impact of the US sanctions also will depend ultimately on the extent of West European and Japanese support for them. But the seven-point program announced Dec. 29 is likely to hurt the Soviet Union in two important areas:
* It may complicate construction of a huge pipeline that is to funnel Siberian natural gas to Western Europe. The Soviets anticipate that the multibillion dollar project will provide them with much needed hardcurrency as well as stronger ties with West Europe, especially West Germany.
* It will make it more difficult for the Russians to count on future supplies of American grain at a time when foreign grain supplies are more vital to them than ever following their third poor harvest in row.
Specifically, under the Reagan package, negotiations on a new long-term grain agreement are being postponed. Export of oil and gas equipment, including pipe-laying equipment, to the Soviet Union will be subject to new restrictions. Issuance or renewal of licenses for the export of electronic equipment, computers, and other high-technology materials is being suspended.
In addition, negotiations on a new US-Soviet maritime agreement are being suspended, and a new regime of port-access controls will be put into effect for all Soviet ships. All Aeroflot service to the United States will be suspended. And no US-Soviet exchange agreements, including those on energy and science and technology, will be renewed in the near future.
According to top US officials, these sanctions will be reviewed in coming days and weeks, and will be added to if necessary to push Moscow toward a change of policy on Poland. US officials have also asked the Western allies to take parallel steps or at least not to undermine the US action.
Even without these sanctions and those the US imposed against Poland last week, the ongoing Polish crisis is a drain on the Soviet economy that threatens to get worse.
Perhaps one of the few bright spots is that the crisis has come at a time when the Soviets' stocks of prized hard currency were apparently doing well. The world oil market, until this year's glut, favored sellers. Moscow is an important seller.
And although Soviet oil production is leveling off, huge stocks of natural gas seem a realistic substitute as a hard-currency earner in the years to come. Recent announcements here say that the world's largest known natural gas deposit , at Urengoi in western Siberia, has been found to be twice as large as originally thought. The gas for the new pipeline will come from Urengoi.
The bad news for the Kremlin is that the Polish crisis came at a time when the Soviet Union, for the first time in the postwar era, is coping with three bad grain crops in a row. Shortages of meat and dairy products have been worsening.
One recent Soviet radio report said shortages of feedgrain in the Ukraine were ''affecting the productivity of animals, their reproduction, and the fulfillment of the meat and milk delivery plans.''
In what some diplomats here took as a reference to Soviet food problems, a prominent Soviet journalist wrote in Pravda recently: ''We have somehow become accustomed to expect that tomorrow will inevitably be better than today.'' But will that happen year after year, he asked rhetorically. The reply: ''Let us speak frankly. That cannot always be achieved.''
To counter such problems, the Soviets have been contracting for large grain shipments from various foreign suppliers - including the US, following Mr. Reagan's cancellation of a Carter-era embargo. Soviet grain imports this year are expected to reach a record level.
It is against this background that the Soviets have been supplying aid to keep Poland's battered economy running.
By Polish estimates, Soviet aid since the turbulent summer of last year has totaled more than $4 billion. This has come in the form of cash transfers, some of them in hard currency, cut-rate oil deliveries, and tolerance of Poland's default on its own export commitments to the Soviet Union.
The Soviet Union also agreed recently to ship Poland 60,000 tons of meat and fish, 10,000 tons of rice, and 100,000 tons of grain. Moscow radio reported this in a Polish-language broadcast for Warsaw. But, perhaps in light of food shortages at home, it did not carry the item domestically.
Soviet officials clearly hope that the imposition of martial law in Poland will gradually revive the Polish economy - and obviate the need for a Soviet military role there that would surely trigger wider foreign sanctions against Moscow.
Any Soviet military intervention would also call into question the repayment of the Poles' $26 billion debt to the West.
Already Western bankers have taken a hard line on Poland's request for emergency help in meeting an end-of-year interest deadline on its huge debt to the West. The evident hope behind the bankers' approach is the the Soviets will feel pressure to dig into their own coffers for the $350 million in hard currency.
In the interim, one official said on Soviet television, Moscow is continuing emergency shipments of oil and other resources. These, according to reports from Poland, include food deliveries.
Some diplomats say the Polish crisis may also help explain a Soviet report of a backlog of grain ships at an important Baltic delivery point. In the past, they say, some grain ships might have docked in Poland, with Polish railroad cars toting the cargo the rest of the way to the Soviet Union.
And Western news media reports that the Soviet Union will make slight trims in its oil exports to some East European allies next year may reflect Poland's strain on the Soviet economy, diplomats say. Moscow may want to sell a greater portion of its oil to hard-currency customers, or it may be allowing for further emergency oil deliveries to the Poles.
With one collective eye on Poland, the Soviets are meanwhile trying to deal with what have become chronic instances of inefficiency, corruption, or both, in various sectors of the domestic economy.
There has been talk in the official media of various sorts of reform: tougher penalties for economic corruption, higher incentives for workers who work well, and a ''food program'' to improve organization and production in agriculture.
No one here doubts the efforts are serious. But both Western and Soviet analysts suggest that radical changes are not likely, and that results are apt to come slowly.