Within a matter of weeks, seven major Japanese companies, noted for their efficiency and technological expertise, have been cited by U.S. government agencies for alleged or suspected spying and cheating to get ahead.

Coming at a time of resentment against Japan for its economic gains at the expense of U.S. companies and workers, the cases could create the impression among Americans that dishonesty rather than business skills are responsible for the Japanese success.

To many Japanese, the cases appear to represent an effort by the Reagan administration to discredit them, according to accounts in prominent Japanese journals. But according to a high-ranking U.S. trade official, the string of enforcement actions within a short period was merely "serendipity." In both nations, however, there is concern about how the cases will affect U.S.-Japan relations.

In the first incident, the result of an FBI "sting" operation, Hitachi and Mitsubishi Electric were accused on June 22 of conspiracy to steal proprietary technical information from their U.S. competitor, International Business Machines Corp. The second case, a few weeks later, found the American subsidiary of Mitsui Corp. pleading guilty to conspiring to sell illegally cheap steel here.

Then, last week, the Justice Department said it is investigating six major Japanese companies to determine if they illegally fixed prices for the 64K random access memory chips essential to the semiconductor business. The companies being investigated are Nippon Electric, Hitachi, Toshiba, Oki Electric, Mitsubishi Electric and Fujitsu.

While government trade officials insist the cases were a coincidence--albeit a happy one to some officials--and were not part of a concerted trade policy against Japan, other analysts say some of the cases were spawned by feelings within the government that Japan's aggressive march in high technology had to be slowed.

"It is clear around the government there's a mood that the Japanese are a serious threat to high technology" for U.S. companies, said Harald B. Malmgren, a former deputy U.S. trade representative, now an economic consultant.

"There's a pattern of feeling that something has to be done to put the brakes on the Japanese."

But Commerce Undersecretary Lionel Olmer says "it is a coincidence" that the cases surfaced at the same time. "It's not an agreeable thing, but I'm darn glad we proved the case against Mitsui" and found them to have violated U.S. trade laws, he added. "I am glad the Customs Service caught that."

"The Japanese cases came together and it looked like we were having some vendetta," Treasury Secretary Donald T. Regan conceded. But he said that the administration was trying to smooth relations with Japan. "It was not part of foreign policy, it was not a part of economic policy."

However, the cases could affect U.S.-Japan relations. Some Japanese have said their image in the United States may suffer, that Americans will believe they are underhanded. American trade officials insist that the Japanese are no more devious than any other nationality, although they do have a large number of other unfair trading cases against them.

The administration is attempting to determine the fallout of the cases on trade policy, particularly while it is trying to persuade the Japanese to be more cooperative by opening up their markets to American goods.

Regan said the cases probably would be discussed among the world's finance ministers, including Japan's, at a meeting in Toronto in September. And the United States will get some sense of the Japanese feelings toward the issue from a previously scheduled trade mission to Tokyo this week.

"In the long run the effect is neutral," Olmer said. "In the short run you could take your pick--it could make the Japanese very resentful, that the Americans are ganging up on them," or they may feel they must open their markets to compensate for the alleged wrongdoing.

All of the cases involve areas of intense competition between the United States and Japan. For example, Japanese firms like Hitachi have reached a dominant position in the world market for computer parts and semiconductors. Steel is a very sensitive area on both sides, particularly since unemployment in the United States is high.

But the three incidents may be a signal of the cutthroat competition the United States may face in other fields as other parts of the world, particularly Japan, catch up with U.S. technology and look for an extra advantage.

"The problem will get worse and worse," Malmgren said. "We're so used to the Japanese copying and following, but now they're getting to the cutting edge of the future."

While Olmer and other trade experts said the Japanese are no more dishonest than any other people, Commerce Department figures show they have been found to have practiced dumping more than any other country. (Dumping is injuring a domestic industry by illegally selling a foreign product in the United States at a price below what it would be sold in the home country.)

Of 82 antidumping findings in effect, 25 are against Japan. The next closest violator is France, with eight findings. Of 108 antidumping reviews under way, 41 are against the Japanese. The cases involve portable typewriters, bicycle speedometers, television receivers, steel wire ropes, fishnet and electric transformers.

The next area ripe for violations, Malmgren said, is machine tools for building high technology equipment.

"It may well be that things are more competitive now," a State Department official said. "In all cases, people are looking for that competitive edge."

"There's so much increasing trade with Japan that perhaps one would expect some problems," said Alan Wolff, former deputy U.S. trade representative. He said, however, that he sees no pattern in the cases.

"There's a lot of pressure on in trade. The competition is very sharp, but competition's been sharp for centuries."