For those who expect changes of government to be followed by sharp changes in policy, Masayoshi Ohira is bound to represent a disappointment.

If his first moves as prime minister are a gauge, he will not offer any spectacular diversions in the economic arena. He doesn't intend any major shifts that would send the American dollar scooting up or down. He hasn't mentioned any tactics that could dramatically lower Japan's trade surplus. He bills himself as a slow-growth man in economics but the path he's choosing doesn't seem all that different from his predecessors.

The signs may be misleading and may reflect only the instinctive caution of a career bureaucrat and party manager accustomed to thinking hard and long about where he wants to go. Ohira's slow-moving cautiousness is almost a legend in political circles and next to him his predecessor, Takeo Fukuda, seems as reckless as a riverboat gambler.

One story going the rounds com pares him to a character in a Japanese proverb, a man so careful that before crossing any stone bridge he would patiently tap on each part to assess its strength. The only difference, so the story goes, is that Ohira taps every stone on every bridge and does not cross any of them.

One high-level government official said recently that if Ohira differs from Fukuda in any significant way it is merelly in matters of style. Ohira is not the type, he said, to go to international summits and pledge his country to unlikely goals, as Fukuda did at Bonn last year in promising a 7 percent growth rate. If there is any constant thread running though his statements so far, it is Ohira's sense of the limits to what governments can accomplish.

Like every Japanese prime minister, and like just about every other world leader, Ohira thinks the American dollar should stay strong as the main force in currency stability around the world. What he would do if there is another run on the dollar next year, like the one last year's not clear. He has suggested that the Japanese yen could play more of a "supplementary" role, taking some pressure off the dollar. Surplus dollars, he has asserted, might be absorbed through the use of more of the International Monetary Fund's special drawing rights. Some expect Ohira to offer some alternative to free-floating currencies during the Tokyo summit next summer, but no one seems to have an idea what it will be.

In the field of foreign trade, where Japan's big surpluses anger the rest of the world, Ohira may not face the rugged tests that Fukuda did. Japan' trade surplus in the current fiscal year ending in March is still a whopper and is likely to end up at the $15 billion mark. But when measured in yen or by actual volume, Japan' exports are tapering off, although they will continue to rise in dollar terms for several more months, most authorities believe.

Some of the more aggravating trade issues have been settled. Japan has agreed to import more agricultural products, enough to take the edge off the American charge of closed markets, but not enough to satisfy Robert. Strauss, President Carters trade negotiator, completely. Automobile exports are still drifting downward. Shipments of color television sets are within the limits negotiated with the U.S. One official of Japan's ministry of international trade and industry observed recently that only one specific export item -- semicon-cuctors -- is likely to cause a trade cruch in the coming months as the U.S. and Japan get closer to a trade war over computer-ware.

Some optimists even dare to suspect that the old criticism of Japan's import policy may be buried in the coming year. It is widely assumed that Japan's domestic market is arbitrarily closed to foreign manufacturers by an assortment of tricky regulations. But in the past six months Japan's imports have risen. True, the European exporters have benefitted more than Americans, but that isn't Japan's fault. Some of the increase is rather artificial, reflecting Fukuda's decision to escape the international heat by "emergency" imports through government purchases, but not all of it by any means.

The big question in many minds is how forcefully Ohira will act to stimulate the Japanese economy and increase domestic demand. Some economists have contended all along that this -- rather than artificially raising imports and lowering exports -- is the key to resolving international trade friction. If the supposedly lush Japanese consumer market is greatly expanded, it is argued, the demand would be enough to wipe out the balance of payment problems gradually.

Ohira's track record in the field of economic expansion is murky and full of conflicting signs. His reputation was built in Japan's high-growth days of the 1960s and Ohira was an enthusiastic supporter of prime ministers who wanted the economic engines to run faster and faster. But in the past year, as he built up his campaign against Fukuda, Ohira has argued that the old days of high growth are over. He thought that Fukuda's 7 percent growth target was unrealistic; in fact, he has opposed even the idea of establishing percent-age targets and then gearing the national economy to reach them.

On the other hand, a couple of Ohira's cabinet appointees are high-growth advocates, prompting some to suspect the new prime minister is not so wedded to cooling off the engines. Furthermore, Japanese newspapers report that, after considerable internal bickering, the new government has settled for a growth target of 6.3 percent next year, which is higher than many prominent economic researchers think possible without more stimulants in the meantime.