LOS ANGELES (AP) _ Experts in Japanese business practices were startled Thursday by charges that executives of a huge U.S. subsidiary of Japan's Shuwa Corp. beat and sexually harassed employees here.

''It would be hard for me to presume that those allegations could be true,'' said William Ouchi, a professor at UCLA's Anderson Graduate School of Management and the author of ''Theory Z - How American Management Can Meet the Japanese Challenge.''

The assertions were made by former employees of Shuwa Investments Corp., which has made headlines by buying the Arco Towers in Los Angeles, the ABC Building in New York and the former U.S. News & World Report headquarters in Washington.

Accountant Hajime Tanioka says in a Superior Court suit filed last week and amended Wednesday that he was repeatedly assaulted by Executive Vice President Takeshi Shiratori and President Takaji Kobayashi of the Los Angeles- based firm. Kobayashi's father founded the parent company.

And in a suit filed late last year in Superior Court, former company secretary Dawn Marie Stover says she was pinched, slapped, fondled and ogled by Vice President Kiichiro Kobayashi, the cousin of Takaji Kobayashi.

Kiichiro Kobayashi denied the allegations and in turn accused Ms. Stover of beating him and berating him with derogatory and racist epithets.

Calls to Shiratori and Takaji Kobayashi were referred to lawyer Craig B. Jorgensen, who said that although he had yet to see the Tanioka lawsuit, from what he knew of the claims, ''I think they are false and we're going to defend it vigorously and I think we'll win it.''

Ouchi, whose research has taken him to Mazda and Toyota auto plants, a Sony TV factory and the offices of many Japanese corporations in the United States, said: ''It would be exceptionally unusual for a manager to strike a subordinate.''

''There's a great deal of formality in most of the social relationships (in Japan), whether at work or in the community life outside of work, and touching another person is a much more socially aggressive act than it is in the U.S.,'' Ouchi said.

''Typically, the Japanese executives here treat their American subordinates with, if anything, slightly more respect than is typical in Japan because in a sense they are guests here in our country and they recognize that and they tend to be extra polite.''

Dennis Laurie, who interviewed 201 Americans working at 21 Japanese companies while preparing his doctoral dissertation at the Peter F. Drucker Graduate Management Center at the Claremont Graduate School, said the allegations, ''if true, are an absolute anomaly.''

''I saw nothing like this,'' Laurie said. ''That's not to say there weren't cultural differences, but the Japanese maintained very cordial relationships with their workers here, particularly with the women.''

Laurie said Japanese managers here are well aware that their actions will be scrutinized more closely than those of Americans, and agreed that many are more cautious than they would be in Japan.

''Everything I've seen indicates they'd double their efforts in a precautionary way.''

In his lawsuit, Tanioka says Takaji Kobayashi struck him with a telephone and calculator, punched him in the stomach and threw a set of keys at him when Kobayashi learned that Tanioka was seeing a former employee.

Tanioka alleges that Kobayashi struck him on the head with a book while the accountant was recovering from an eye injury after Tanioka refused to work overtime.

The suit also alleges that Shiratori hit the accountant with a ruler and rolled up newspapers and magazines. Tanioka, who says he was forced to resign from the company, also says he repeatedly was verbally abused and called ''fool'' and ''idiot.''

Ms. Stover, who quit in 1988, alleges that Kiichiro Kobayashi made sexual suggestions as well as hitting and touching her and striking her with rulers and other objects.