1981 trade tilt favoring East bloc over West has Yugoslavs concerned.

''Neither Yugoslavia nor the United States is happy with our [1980] trade,'' laments Gojko Tesanovic, managing director of the Yugoslav export firm Interexport. ''It was $1.4 billion [in 1980], out of which $1 billion was purchased in the US, and the remaining $400 million was US purchases in Yugoslavia.''

The US-Yugoslav balance is not untypical of Belgrade's trade with the West as a whole, and this is what concerns Yugoslavs. They exported only $2.9 billion to Western Europe in 1980, while importing more than double that amount: $6.6 billion. Their performance in 1981, even after the 1980 trade agreement with the European Community, has been no better.

Exports to the West drooped in the first six months of 1981. From Jan. 1 to June 15, countries in the Organization for Economic Cooperation and Development received 4 percent less in imports from Yugoslavia than in the 1980 period. In contrast, exports to the Soviet bloc flourished, with a real Jan. 1-June 15 rise of 64 percent and a modest Yugoslav surplus of exports over imports. For this maverick communist country that once had to withstand Stalin's attempt to strangle it by economic boycott, such a degree of trade dependence on Moscow is a serious development:

* It intensifies the 1980 trend of falling exports to the West (47 percent of total 1980 Yugoslav exports, down from 55.3 percent in 1979).

* It emphasizes rising exports to Comecon countries (36 percent of total exports in 1980, up from 30.4 percent in 1979.) Comecon is the East-bloc trading counterpart of the European Community. The Soviet Union alone jumped from 16 percent of total two-way trade and 21 percent of Yugoslav exports in 1979 to 21 percent of total trade and 27 percent of Yugoslav exports in 1980.

Yugoslavia is also increasing exports to developing countries (17 percent in 1980, up from 14.3 percent in 1979 and 15 percent in 1978).

The causes of the growing imbalance are simple enough. Economic recession has made the West choosier about its imports and prices. And Yugoslavia's economic base is too small for its unit costs to be competitive with the large-market US or EC costs - or cheap-labor third-world costs. At the same time Yugoslavia has to sell more to the Soviet Union to pay for higher oil prices - and a Soviet Union that is starved for consumer goods will buy virtually anything Yugoslavia produces in this line.

Since Yugoslavia has no desire to return to economic dependence on the Soviet Union, the solution is far from simple. It involves making Yugoslav exports attractive in design and competitive in cost with Western European, Japanese, South Korean, and Brazilian goods.

Many export items do meet the test. Mr. Tesanovic cites motor parts and tools that Yugoslavs sell to the US, as well as the $69 million worth of wooden furniture, which was the largest item sold to the US in 1980.

He relates in passing that on a recent trip to his company's New York and Long Beach, Calif., offices he stopped off in a Chicago department store to look for a gift to bring back to his daughter. He found the perfect windbreaker - only to discover a made-in-Yugoslavia tag.

There are still a lot of Yugoslav products that haven't caught on in the American market, however. Tesanovic would like to get hemp exports back up from their 1980 slump, in which they fell below the top-10 exports, to their 1979 level of $75 million. He would like to see McDonnell Douglas and Boeing buy many more parts from Yugoslavia. Interexport itself has bought 11 DC-9s and Yugoslav Airlines has 30 American-made aircraft. He would also like to sell America more fruit juice, shoes, and ready-made clothes.

What are the chances that Interexport and the several hundred other export firms can in fact significantly boost their sales of such products in the West? Not very good in the short run, according to some top opinion here. The managers of the 70-odd leading export companies optimistically set a target this past summer of 7 percent real growth in 1981. But specialists like Vinko Mir, federal assistant secretary for foreign trade, think the final 1981 figures will show something more like a 9 percent real drop.

Over the longer run Yugoslav officials hope to inrease sales to the West by stabilizing export regulations (currently subject to yearly fluctuations) and also by attracting more Western joint ventures. Yugoslavia was the first Eastern European country to permit direct foreign investment in local enterprises, 15 years ago. And it liberalized legislation in 1978 to allow joint ventures in all sectors except insurance, commerce, and social services.

By now more than two dozen US-Yugoslav joint ventures exist, constituting roughly 40 percent of the still low foreign investment in the country. The largest of these, the eight-factory Dow Chemical-INA (Industrija Nafte, a Yugoslav company) petrochemical complex on the island of Krk, contributes significantly to Yugoslavia's second-largest export category to the US ($41 million in 1980) of naphtha and petrol. Naphtha, a derivative of petroleum, is used in production of other petrochemicals.

Yugoslav officials hope especially that American companies will establish joint ventures here for sales to other countries. This kind of arrangement already exists on a small scale, with Interexport acting as an equipment subcontractor for hotel projects in Egypt and other projects in Algeria involving American credits and designs.

The field is wide open to more deals of this sort, officials suggest. They stress the advantages of available lower-cost skilled and unskilled labor; nonaligned good relations with the third world; Yugoslavia's rich experience in intermediate technology in demand in developing nations; and its geographical location near the Mideast and Western Europe.