Chevron Corp. has spent three years and untold millions of dollars examining the possibility of developing a major oil field in the Soviet Union, but the odds are no better than 50-50 that the San Francisco-based oil giant will go ahead with the deal.

The cost, and operational and political risks, may be too high, said Chevron Vice President Edward B. Scott.

"There are still an awful lot of things that have to be done," Scott said in an interview.

Chevron isn't alone in testing the Soviet business waters and finding them a bit rough. Businessmen from around the world have flocked to Moscow since Soviet President Mikhail Gorbachev encouraged them in 1986 to seek joint ventures with Soviet partners.

Gorbachev's strategy, in part, was to revitalize the bankrupt Soviet economy by introducing modern technology and Western business methods. The foreign companies were attracted by the notion of getting an early toehold in a largely undeveloped market of nearly 300 million consumers.

So far, the reality has failed to match the hoopla. U.S. officials estimate that about 1,300 joint ventures have been registered with the Soviets -- 140 of them involving American companies -- but only about 200, or less than 15 percent, are operating.

It is against this sobering backdrop that Gorbachev is expected to stress during his visit here next week the need for greater trade and investment with the Soviet Union. He is likely to strike that theme here, in Minneapolis and in California -- even though the expected signing of a U.S.-Soviet trade agreement appears to have been derailed because of Moscow's economic blockade of the breakaway republic of Lithuania.

But the lesson from the experience of Chevron and other foreign companies is that doing business with the Soviet Union is not easy. It takes big bucks, time and patience to deal with a recalcitrant bureaucracy unused to capitalist ways and a society so riddled with shortages that getting materials for a manufacturing plant is a daunting task. Adding to the downside, the chances are slim of getting profits out of the country in hard currency any time soon.

Another, major problem also has exploded for companies over the past six months as the Soviet Union, known for decades as a country that paid its debts on time, has fallen far behind in its payments to Western suppliers. No one knows for sure how large the outstanding debt is, although estimates place it as high as $8 billion, or 10 percent of the value of all Soviet imports.

Western officials and businesses are unsure whether the falloff in payments is due to bureaucratic snafus, as the Soviets claim, or if the country is in the midst of a basic cash flow problem. {See story, Page H6.}

Chevron's Scott noted that many problems arise after initial deals are struck and the realities of doing business with the Soviets scrape away initial enthusiasm.

"Many joint venture agreements don't cover all the bases. Companies enter into them and then see the pitfalls. That is why so many joint ventures never go further than the signing of the document," he said.

"They rarely come to anything," said J.M.C. Rollo, head of economics at Britain's Royal Institute of International Affairs. "Who can you deal with? You never know who is in charge. Once you get a {Soviet} partner, you find there are another three or four layers of bureaucracy."

Stanislav V. Assekritov, deputy chairman of the USSR Council of Ministers State Commission for Economic Reform, candidly admitted in a recent speech to American businessmen in Washington that "numerous blocking factors" exist in doing business with Moscow. He identified four main ones: the inability to convert Russian rubles into hard currency; the lack of laws protecting foreign investments; an "overly bureaucratic" decision-making system; and the absence of a capital market that allows foreign investors to raise money in the country.

He emphasized that Gorbachev, who wants to increase trade and foreign investment, is trying to make things easier for businesses.

He has a lot to do.

Although there have been some successes, there have been many more major deals that are stalled. Chevron, for example, is a member of a highly publicized American Trade Consortium that includes RJR Nabisco Inc., Eastman Kodak Co., Johnson & Johnson and Archer Daniels Midland Co., as well as the Mercator Corp., a New York merchant bank headed by ATC President James Giffen. It announced more than a year ago that it had reached a trade pact with Moscow that would quickly clear the way for investment of as much as $10 billion in 25 joint ventures.

So far none has emerged.

A seventh member of the consortium, Ford Motor Co., which was considering opening a modern auto manufacturing plant in the Soviet Union, pulled out before the trade pact was signed in March. It said the agreement failed to provide the depth of financial guarantees needed to support the cost of opening a giant auto manufacturing plant.

Similarly, Siemens AG thought it had a deal last June to sell 200,000 personal computers to Russian schools, giving the West German electronics giant a major head start on its competitors. The arrangement foundered on financing, with the Soviets unable to find a barter partner that would provide the hard currency to pay for the computers, company officials said last week. But they are still trying, and Siemens refused to call the deal dead.

The classic deal for getting dollar profits from Soviet ventures is a barter agreement, PepsiCo's 18-year, $3 billion-a-year arrangement to swap Russian-made Stolichnaya vodka for Pepsi. Last month, Pepsi extended the deal for 10 more years and expanded it to include the purchase of 10 Soviet-made freighters for sale on international markets. The new arrangement will allow Pepsi to increase the number of its Soviet bottling plants from 24 to 50.

Similarly, the American Medical Consortium signed a new joint venture last week to make medical, surgical and dental instruments that allows the consortium to export 20 percent of production for hard currency, despite a shortage of medical supplies in the Soviet Union. The group also operates a medical clinic in Moscow, which will cater to foreigners there, drawing in more hard currency. And Federal Express, a member, earns dollars from its shipments.

Consortium President Dennis A. Sokol said that other members -- Colgate-Palmolive Co., Hewlett-Packard Co., Hospital Corp. International, Medical Services Partners and Pfizer International -- had developed such good relations with their Soviet partners that they had made $40 million to $50 million in hard currency sales before their joint ventures were completed.

The most visible Western success in Moscow is McDonald's, which serves 50,000 people a day at its recently opened Moscow restaurant and now is seeking sites for five new branches. Not considered a high-technology operation in the United States, McDonald's was welcomed as an example in modern management, food processing and production techniques -- all in short supply there. And the fast-food restaurant provided a diversion for Moscovites who have too many rubles and not enough goods to spend them on.

"They have tremendous disposable income," said George Cohon, head of McDonald's Restaurants of Canada Ltd., which runs the Moscow operation. "So in walks McDonald's with a ruble restaurant ... They are seeing things they don't see anywhere else in the Soviet Union."

In the process, McDonald's is earning large ruble profits, Cohon said, and has a head start on a potential market of 300 million Russians. Further, it is finding ways to sell its excess production of pasteurized milk, French fries and apple pies to foreign embassies and hotels catering to foreigners -- all in hard currency.

McDonald's has become such a tourist site in Moscow that Secretary of State James A. Baker III took a private nighttime stroll down Gorky Street during his visit to Moscow 10 days ago to see for himself. He didn't grab a Big Mac -- the line was too long and there is a strict McDonald's rule against queue jumping but he stayed around to talk to the diners.