President Reagan and the other heads of government are gearing up for a mostly self-congratulatory economic summit in Tokyo early next month, glossing over real problems that divide them on trade, the levels of economic expansion in Europe and Japan, and how to deal with the Third World debt issue.

They also will have to finesse the sharp difference between the United States' friendly evaluation of Japan's newly announced determination to focus on imports instead of exports and the continuing hostile and suspicious attitude of Europeans toward the Japanese.

The upbeat attitude on the global economy is based on the collapse of oil prices, lower interest rates and the prospect that the world as a whole can contemplate extraordinarily low inflation rates for a number of years.

In an interview last week, Secretary of State George Shultz said that "there is an underlying, rather positive, tone to things." After a visit here with President Reagan, Japanese Prime Minister Yasuhiro Nakasone said that the two leaders "shared the view we should work together to send from the Tokyo Summit a message of bright prospect" for all the peoples of the world.

As Treasury Secretary James A. Baker III noted at the recent session here of the World Bank and International Monetary Fund, the cheaper dollar, combined with other favorable indicators, is producing "the best economic environment" for Third World countries since 1970.

For oil-exporting countries such as Mexico, the drop in the price of oil from the $30 to the $10 range since November is a shock. And per-capita income continues to decline in sub-Saharan Africa. But for the rest of the world, the oil price collapse is a bonanza of huge proportions. And in the United States, cheap oil also helps to offset the inflationary impact of the sharply declining dollar.

Meanwhile, a dollar more in line with other major currencies improves the competitive outlook for American industry and promises some reduction -- eventually -- in the huge U.S. trade deficit, softening harsh protectionist voices in Congress.

Yet more fallout from the dollar's decline is the weakening of the demand that had been accelerating in Europe and in the U.S. Congress for international monetary reform, or some new global Bretton Woods conference that might lead to a return to a fixed-rate system.

Baker and other finance ministers at the IMF meeting threw cold water on the idea of a monetary conference. The most that is likely to come out of the Tokyo summit on that issue is approval of continuing studies of "improvements" in the present system.

The ambivalence about monetary reform is seen in a murky description Baker offered of the objectives for any new system. It should have qualities of "flexibility" and "automaticity," the secretary said. In similar fashion, Nakasone told a press conference that Japan rejected the concept of "target zones" -- a system in which nations would agree to keep their exchange rates within fixed parameters -- but with hoped-for "managed flexibility."

The contradictions implied in these terms was reminiscent of former French prime minister Raymond Barre's proposal in 1977 for a system of "organized free trade," a fruitless effort to blend protectionist and open-market principles.

In any event, France now appears isolated as an advocate of immediate reform of the monetary system -- and with a stronger franc and an improving domestic economy, the French will be less anxious to press their traditional assault on a dollar-denominated world in Tokyo.

Behind the note of relative euphoria and comfort with the way things are going, however, lurk growing European-American strains over trade issues, and Japan's huge balance-of-payments surplus.

American officials have been accusing Europe of increasing protectionism, especially over agricultural products. Undersecretary of State Allan Wallis -- the U.S. "sherpa," or preparer for the summit -- fingered Europe the other day as "probably the most disruptive factor in the world trading system."

The problems caused by Japan's international surpluses will be equally difficult to resolve. When Shultz was asked in the interview to name the most difficult global economic issue, he unhesitatingly pointed to the "gigantic" $49 billion current account surplus run up last year by Japan, reflecting a trade surplus of an even larger amount.

It wasn't much noticed, but Reagan and Nakasone agreed at their Camp David session that there would be "a bilateral dialogue of high officials on structural problems." Informed sources say this means that Shultz and Baker for the U.S. side and Foreign Minister Shintaro Abe and Finance Minister Noburo Takeshita for the Japanese side will take direct responsibility to manage overall U.S.-Japan economic differences in an effort to bypass their respective bureaucracies.

A recent blue-ribbon advisory group headed by former Bank of Japan governor Haruo Maekawa recently recommended that Japan switch from an export-or-die society to one dependent on domestic demand. The report pulled no punches, and Nakasone endorsed the main theme: The huge trade surplus is unhealthy and undesirable.

Japan is prepared to suffer considerable pain -- and political opposition -- to carry out the recommendations of the Maekawa report, according to officials who traveled here last week with Nakasone. For example, it is prepared to close 10 out of 13 major companies in its inefficient coal industry -- throwing miners out of work in the Hokkaido province -- while importing cheaper coal.

But as a former ambassador to the United States, Yoshio Okawara, said earlier, a transformation of the scope envisioned by the Maekawa report will take a minimum of five to seven years. The ruling Liberal Democratic Party is not too happy with its sweeping recommendations.

With low unemployment, establishment leaders can take on distressed domestic industries such as coal; but to reduce agricultural protection and to boost farm imports, as the report suggests, "has been a taboo that no one in the past has dared to touch," Okawara observed.

It is easy to be cynical -- as are the Europeans for the most part -- and to believe that nothing will come of it. Just prior to the publication of the report, the highly respected Peter F. Drucker wrote: "The Japanese only sell; they do not buy. They practice adversarial trade."

There continues to be a strong body of opinion among the Japanese that they shouldn't be blamed for working harder and doing a better job than their competitors in world markets. In his 1983 book, "The Japanese Mind," Robert C. Christopher, a student and long-time friend of Japan, wrote that "most Japanese, in their hearts, feel superior to the rest of the world."

That still may be true, but the Maekawa report, which has strong support within the Japanese business community, could mark the beginning of a historic new era in Japan. Another one of Christopher's seven "basic" propositions about Japan is that "Japanese find it easier than most peoples to accept change -- and sometimes do so simply so that Westerners won't think them 'backward.' "

But the summit leaders won't have time to deal with these tough economic issues. They are likely to be preoccupied with terrorism and other noneconomic problems. For host Nakasone, the name of the game will be to pledge cooperation with the other major nations and hope to deflect pressure from the Europeans for a further appreciation of the yen. He'll sigh with relief as everybody heads to Narita airport and home.