US, Japan jointly venture into carmaking. From morning exercises to company uniforms, American automakers are learning the Japanese way of making cars. Meanwhile, Japanese companies operating here are trying their hand at American labor relations.

A new car, built in a new plant, by new workers, under new management. That, says Katsuhiko Kawasoe, is the challenge two leading car manufacturers - one Japanese, the other American - face in the gleaming assembly plant they have built in the cornfields of Illinois.

Honda, Nissan, Toyota, Mazda, and now Mitsubishi - the procession of Japanese carmakers setting up plants in the United States is long. Some alarmed Americans speak of a Japanese ``invasion'' taking jobs away from established American car companies.

But Mr. Kawasoe insists that Diamond-Star Motors, a 50-50 joint venture of Mitsubishi and Chrysler, is different from other wholly or partly Japanese-owned plants.

``First, we're making a brand-new car, never built either in Japan or in America before,'' says Kawasoe, an executive vice-president. ``Second, the plant is new, full of technology including types of robots that we haven't used before. So naturally we need new workers and a new style of management.''

``Of course, we think first how we build cars in Japan. But then we ask ourselves, `To what extent can we really transfer these methods to America?' That's when we consult with our Chrysler partners. Every decision we make is by consensus. Admittedly, that takes time.''

Says George Hohendorf, also an executive vice-president at Diamond-Star, ``The Japanese style of management is a refresher course on what we should have been doing all along.'' According to Mr. Hohendorf, Chrysler's main purpose is to learn how the Japanese make cars.

``We taught them first. They did their homework well, while we have to come to grips with the fact that we became careless, because we could sell cars even if they weren't perfect. We have to get back to the basics.''

Hohendorf notes that Chrysler brings its own strengths to the project - tremendous engineering know-how and a proven management team that has brought the company back from the edge of bankruptcy to renewed prosperity.

Kawasoe is short and chunky, Hohendorf a rumpled bear of a man with traces of a German accent from his native Transylvania (part of Romania), but the chemistry between them is good. Like other members of Diamond-Star's top management team, they have had to learn to communicate across formidable barriers of language, customs, and culture. Only one of the four top executives from Mitsubishi is totally fluent in English.

``We understand each other's words reasonably well, but it takes much longer to share meanings,'' Hohendorf says. ``We have to put a lot of things in writing.... Communication is difficult, but not impossible. For instance, I speak a lot more slowly than I used to.''

Kawasoe and Hohendorf are part of Diamond-Star's management team, in which the chairman, Glenn Gardner, comes from Chrysler and the president, Yoichi Nakane, from Mitsubishi. Kawasoe is responsible for administration and personnel; Hohendorf is senior manufacturing adviser.

The companies have agreed that Mitsubishi will take charge of plant design, construction, and production engineering, while Chrysler looks after vehicle durability and development testing.

Both companies took part in designing the new car that Diamond-Star will produce - a snazzy, front-wheel-drive sports coupe code-named the X2S.

The assembly line will start rolling in August. In 1989, a four-door sedan will be added to the production mix. When the plant, which cost $650 million shared equally between the two partners, reaches full capacity two years hence, it will be churning out 240,000 cars a year, half to be sold through Chrysler and half through Mitsubishi.

It is a few minutes before 7 a.m., and in a corner of the spotless cafeteria, a 17-man group headed by mustachioed Ray Robinson has assembled for ``morning exercises'' and a brief meeting before going to work stations. These are maintenance people - skilled workers learning how to care for state-of-the-art robots at key points on the assembly line. They are dressed in dark gray trousers and maroon work shirts, a costume that George Hohendorf also wears in his executive office.

A catchy tune ripples through the loudspeaker system and about half the men stand up and go through some mild gymnastic exercises. Two Japanese ``technical advisers'' are the most vigorous. Some of the Americans move almost as briskly; some seem a bit sheepish. The nonparticipants sit and look on amusedly. Evidently the exercises, normal in a Japanese company, are controversial here. ``We don't force them on anyone,'' says Mr. Robinson, who spent 10 months as a trainee in Japan.

In two minutes the exercises are over and Robinson, the ``group leader'' (the others are ``associates'') goes through the day's schedule and commends a team member who discovered a short circuit and devised a plan to correct it. ``Good job. Good research,'' he says, as the others applaud.

This is on-the-spot kaizen, or improvement suggestions, another normal Japanese practice. So far the plant has built only test models.

Production has not yet really started, and there are only 750 employees, compared with a final planned figure of 2,900. But from the beginning, quality circles and kaizen have been integral parts of the work environment. In May, says staff engineer Mike Carbaugh, 49 associates turned in 149 kaizen proposals.

``Before I went to Japan,'' Robinson says, ``I thought the Japanese were regimented and autocratic.'' But the people he met were open and friendly, and he sensed no constraint about their kaizen activities. Robinson, who spent 17 years maintaining machinery at a meatpacking plant, says he is pleased and proud to be working at the leading edge of carmaking technology.

Nobuo Tomita, one of the technical advisers to Robinson's team, is a tall, craggy veteran with 28 years of maintenance experience at Mitsubishi.

``We're really jacks-of-all-trades,'' he says at an evening session back at his dormitory. ``So-and-so might be an electrician, so-and-so might be good in mechanics, but in this kind of work you've got to be prepared to do a bit of everything.''

That, both he and other Japanese trainers say, is the most difficult thing to teach here. Partly this is because of the strict jurisdictional lines in most traditional labor contracts. It may also reflect a fundamental difference in attitudes and upbringing between Americans and Japanese, the trainers say.

Americans are taught to be individuals responsible for their own actions. They want clear lines of responsibility, usually in writing. Japanese, on the other hand, are used to working in groups and sharing responsibilities.

``At two o'clock in the morning,'' Mr. Tomita says, ``if the robot isn't working and you know you can fix it, do you sit around and wait for the specialist?''

``There's one phrase we're trying to eliminate around here,'' Kawasoe says. ``It's none of my business.'' The phrase may work in some situations, he says, ``but it won't build dependable cars.''

And what do the citizens of Diamond-Star's brand new home think of what Mitsubishi and Chrysler are trying to achieve?

``Most people here think it's a good idea,'' says a motorist giving directions to a lost journalist. He had an uncle, he says, who had fought at Iwo Jima, ``but it's a lot better to be building cars together than to be killing each other.''