The pressures within the worldwide computer industry to obtain International Business Machine Corp.'s plans for rapidly changing products has led to the biggest industrial-espionage dispute between the United States and Japan, computer industry experts said yesterday.

Employes of Hitachi Ltd., the world's largest manufacturer of highly sophisticated semiconductor memory components and the fourth-largest manufacturer of general-purpose computers in Japan, stands accused by the Justice Department of attempting to steal crucial technical data on new IBM products.

Hitachi officials yesterday denied having tried to obtain the information illegally, but Japanese computer company officials were searching for an advance look at IBM technology, according to U.S. industry sources.

As IBM, the world leader in large computers, has increased its rate of innovation, the pressure on competitors such as Hitachi, who manufacture computer equipment that connects to IBM machines, has mounted tremendously, according to industry analysts.

"If Hitachi could have convinced someone to give them information about IBM's new software package for large mainframe computers, they could have beaten their competition to the market with their own duplicate software by six months or a year," said Howard Anderson, president of Yankee Group Inc., a large Boston-based consulting firm that does work for IBM.

"A Hitachi executive came into my office a few weeks ago and asked me to provide him with proprietary information about IBM's new software package for mainframe computers. I told him that information would not be available until IBM released it publicly later this year.

"That software package is worth millions and millions in the marketplace. The only way you can become a power in the mainframe market today is to be com patible with IBM, and this case shows the length and effort that competitors will go to as they try and overcome the IBM advantage."

"A knowledge of what IBM is doing with the new software package would have enabled Hitachi to cut their lead time between IBM's delivery of the package and their own release," Anderson said.

Kenji Hayashi, a senior Hitachi engineer, told undercover agents that two years would be needed for the company to "follow up IBM's architecture" and "design the software," according to the Justice Department. Hayashi was one of the Japanese computer executives charged with paying $648,000 to an FBI undercover agent to obtain the IBM secrets.

In the U.S. market, Hitachi sells large mainframe computers through National Semiconductor Corp. Its share of the $10.8 billion U.S. computer market is slightly more than one percent. IBM dominates the general-purpose computer market, controlling almost 61 percent.

Hitachi's diversification and ability to apply advanced semiconductor research to other product areas are among its chief strengths, according to Karen Stults, an analyst for Morgan Stanley. All Hitachi computers and software systems sold in the U.S. are compatible with IBM equipment.

"Hitachi has developed good technology in semiconductors, and that is showing up in their video products and their robotics" (machines that act like assembly-line robots), Stults said. "They are also experiencing growth in their medical products area."

Hitachi, which had a net income of $537 million last year at present exchange rates, spent about $500 million in 1980 on research.

"The access to IBM technology before it appears on the market is the precise issue IBM is now fighting in Europe with the European Economic Community," said John Diebold, chairman of Diebold Group Inc., an international management consulting firm.

"The EEC has stated that one of its objectives is to force IBM to disclose product development information publicly just as soon as their engineers discover it," Diebold said. "The value of that information for firms developing product lines compatible with IBM is reflected in the substantial sum the Japanese were willing to pay."

"Tactically, this could not have come at a worse time for Japanese industry," Anderson said, citing the growing friction between the two countries over trade issues.