Work on the car assembly line at the Ford Motor Co.'s giant River Rouge plant is a choreographed routine with few diversions. The factory is damply warm and fluorescent and smells like sweat and chemicals. It's too noisy to talk. The wraparound sound is like a special effects movie. Over there, the hiss of welding guns. Further down, the grate of drills against an engine block. Supervisors hovers in their short-sleeved shirts, eight pens to a pocket and a cigarette in each one's mouth.

The line doesn't look or sound much different on a hot summer day in 1980 than it did 67 years ago when Henry Ford put an endless belt over a set of pulleys and started mass producing the Model T.

The Rouge line is the patriarch of Ford's assembly plants, aging and technologically unsophisticated. Yet it is often productive of all the company's 16 car and truck assembly lines, turning out about 70 cars an hour during peak production. Workers can build a Ford Mustang from frame to finish in 45 minutes.

While foreign competitors are racing to stock new plants with the latest in robots and computer programmed welders, the juice that powers this 1,200-foot assembly line is still heavily human.

Technological advancements have been slow in coming to the American assembly line. Many factories, like this pre-Depression era plant, are half a century old or more and Ford's most modern car assemly dates back 23 years. Retooling and modernization of assemblly lines is a costly proposition at a time when the auto industry is mired in debt and doubt about its future.

Chrysler, recently rescued from bankruptcy by the credit of the American taxpayer, announced that it had lost $536 million in the second quarter alone. Ford lost $468 million in the same period, and General Motors lost $412 million.

The Japanese have moved from America's blind spot into a solid 22 percent share of the market. In the last six months of 1979, for the first time in history, Japanese carmakers began to sell more motor vehicles than any other country.

Suddenly, what's wrong with the auto industry is what's wrong with America.

President Carter has gotten involved. United Auto Workers President Douglas Fraser journeyed to Tokyo to "sensitize" the Japanese to growing unemployment here. The word productivity has moved out of the efficiency engineers' manuals and into the American lexicon of trouble.

How does it happen that Japan, which has none of the natural resources that go into an automobile, can build the Corolla, ship it 10 days across the Pacific to the American West Coast and sell it competitively in a country that pioneered the low-cost car?

American and Japanese experts in Japan gave Washington Post correspondent William Chapman varied and complex reason. A major reason is obvious: labor costs are far lower in Japan. When salaries and fringe benefits are tabulated, the American auto worker's compensation is 1 1/2 to two times that of his Japanese counterpart.

Other explanations are more subjective. There is the legendary devotion to work and company of the Japanese employe, a cultural phenomenon that still astounds foreign visitors.

Then, there is the effect of automation, much further advanced there than in the United States. And finally there is the question of management: some people think the Japanese manager may be cleverer and more farsighted than his American peer.

Inside the Detroit assembly plant, on a day that starts at 6 a.m. and ends two shifts later at midnight, the spot welders crank up their guns a half-mile back from the finish line. Bare unpainted car frames swoop down from overhead conveyor belts like ferris wheel cars in an amusement park and tip into a tunnel, where the welders are waiting.

They stand in two lines, eight to a side, looking like bleached-out Darth Vaders in white body suits. The welders jab their torches against the skeleton's joints, sending cascades of blue and silver and gold sparks into the air.

"If you're not a welder at Ford's you are nobody," says one as he shoots his gun 16 times into the curve of a hood.

The car shells are lifted out of the tunnel on two tracks and then branch off, one track to the left, the other to the right. One by one, engines, axles and other components are fed into the line at specific points until the bodies moving on overhead tracks are dropped onto waiting frames. Workers who stand all day in a pit underneath the line, their faces lit up like neon ghosts, check the undercarriages of the passing cars.

Down drops a midnight blue Mustang and three men attack it with drill guns.

One drills straight up from the pit on his 72d Mustang this hour, another attaches some molding inside, another sprays holes into the tailpipe assembly.

It's 90 degrees outside but it feels worse inside the cavernous plant, where big old-fashioned fans spray hot air into hot air. The workers nearest a giant red slude tank are coated with a fine, wet film and the women roll their jean legs up to their knees. Some of the pit men shed their shirts as the heat and humidity turn flesh into sponge.

During the 1968-78 decade, robots developed in Detroit were bought and improved upon in Japan and spread widely through the industry. Nissan, which produces Datsuns, figures one robot equals the work of 1 1/2 human beings and does not need higher wages and fringe benefits.

Precise statistical comparisons are hard to find, but William Chapman found little dispute about the basic fact that the highly automated Japanese plants have climbed past the American ones in the productivity race.

The crudest measurements show an enormous gap. In 1978 Toyota's 45,000 workers produced 2.9 million cars that sold, for a ratio of 65 cars per worker. wGeneral Motors sold 9.5 million cars produced by 839,000 employes, equal to only 11.3 cars per worker. By that guage, the Japanese company was turning out six times as many cars per employe as the American one.

The different industrial structures make such comparisons of dubious value, however. Chapman found that much of the kind of work performed at General Motors or Ford is done in Japan by outside suppliers. The Japanese company buys from outside many of the parts that General Motors makes in its own plants and the per worker productivity does not reflect that.

If all the Japanese supply companie's employes are included in the comparison so that the total worker forces are roughly comparable, the gap narrows considerably.

One analysis by Nissan is based on U.S. Labor Department and Japanese industry figures. The study is revealing not because the gap is wide, but because it shows how the Japanese industry has caught up with and surpassed the American industry in an eight-year period.

In 1969, the Japanese motor vehicle industry and its major suppliers turned out the equivalent of 9.4 cars per person employed. The U.S. auto industry was still ahead, producing 11.2 cars per employe.

During the next eight years, however, the Japanese industry's productivity rate increased an average of 6 percent a year. In the United States, the rate went up only 2 percent a year. The result: by 1978, the Japanese industry was turning out cars at a rate of 14.8 per worker. The U.S. industry had slipped behind to 13.2 cars per worker.

One reason is robots, and the reason behind their introduction tells as much about different management-worker relations as it does about productivity.

"At first we were just putting in robots to do some of the hard work to please the employes," said Nissan director Takeo Arai. "The main reason at first was not to lower costs, but we found out that they did."

In Detroit, the lunch buzzer rings at 10 a.m. and the line stops cold. The plant is so big that most people stay put, eating from brown bags right up against the line, their fingers leaving dark stains on the sandwich bread. Some of them eat or smoke cigarettes inside the cars stranded on the line. One woman sleeps curled up on the back seat of a red Capri.

Everywhere there are crates stacked high with transmissions and tires and air filters and exhaust pipes. Fork-lifts career down the steel tile aisle, dodging miniature trains hauling supplies. Weaving through all this commotion in perfect syncopation, like a Broadway musical, are dozens of foremen riding old-style balloon tire bikes.

Assembly line supervisors are rather like school hall monitors. They are responsible for a certain number of workers on a certain portion of the line, making sure that they behave, that they are doing their jobs correctly, and that the line runs smoothly.

If the line breaks down, which it does often, supervisors make sure it gets fixed. If a worker is absent, supervisors make sure there's a substitute body on the line. The workers, who wave disrespect like a flag, refer to supervisors as "company chowderheads" and are fond of giving them the one-digit salute.

When the line comes back up after lunch, a man wearing a blue work shirt and a red bandana, a cigarette dangling lazily from his lips, moves methodically from car to car. He drills two holes in the engine block and attaches two wires. It takes him about 10 seconds. The next man shoots power steering fluid and windshield washer solvent into the engine compartment and drops in the horn.

Nowhere is the human capacity to absorb monotony and repetition more striking than on the assembly line, although any despair is tempered somewhat these days by massive auto industry layoffs. Workers know that a job on the line may be gone tomorrow, along with the $20,000 that an assembly line worker can make a year, plus fringes like free eyeglasses and free legal help.

More than 1,100 1980-model Ford Mustangs and Mercury Capris were turned out this day by 4,173 hourly workers on two shifts. They were assisted by the efforts of thousands more working in the 205 coke ovens, three blast furnaces, steel mills, foundry, engine plant, stamping plant, tool-and-die plant, frame plant and glass plant which make the Rouge the largest industrial complex in the world.

It is an industrial city that has the capability of producing a car from scratch, or as Henry Ford II likes to say, from "iron ore to assembly line."

There is talk now of giving workers on the line more control over their product. Ford and the United Auto Workers union recently agreed on a precedent-setting quality control program that would enable hourly workers to shut down the line if they spot defective cars on it.

The fact that the automaker is even considering such an innovation is evidence of growing industry concern about product quality and many car buyers' insistence that imports are better made. "It's plain common sense to help the workers get directly involved," says a UAW official.

Ford plans to have 24 computer programmable "robots" working in its Wayne, Mich., and Metuchen, N.J., assembly plants this fall -- most of them fixed-arm machines that are programmed to carry a welding gun and perform a specific sequence of welds on the car body.

Ford has 294 of these robots in use worldwide, most in assembly plants. But executives concede that the Japanese are "moving very fast" in the technological race and "will probably outdistance us."

"The technology of the robot is not there yet to perceive color and pick a stock part from different locations on the line and marry that part with a moving body and then hold the piece while the screws are installed," says Paul Guy, Ford's director of manufacturing, engineering and systems.

"All of those things that a human can do, and do quickly, you are simply not going to get right now from current technology."

Some authorities think that the Japanese decision to invest heavily in higher technology, when Detroit did not, is the real key to Japan's automotive succes story, correspondent Chapman reported from Japan. A rough calculation made by Nomura Research Institute shows what happened. In 1968, Toyota's plants housed about $16,600 worth of equipment for each plant employe and General Motors was already behind with about $11,900 in equipment.

During the following decade, by the Nomura reckoning, Toyota more than doubled that ratio to hit $40,800 in equipment per worker while General Motors actually dropped back a bit.

"To put it simply, the investment had the result of making it easier to make cars. General Motord did not increase its investments. It just kept pace with depreciation," said Yukio Suzuki, and automobile securities analyst for Normura.

Another factor in high Japanese productivity is the subjective one of worker motivation. The Japanese worker has a ferocious devotion to his company and an enormous desire to see it making money and the best products. Nissan's Arai believes this "loyalty en masse" is essential in understanding the Japanese auto company and why it turns out cars of such eviable workmanship.

Occasionally, it even gets out of hand. Arai recalls one incident in which some overzealous Nissan workers insisted that their lines' cars would be even more appealing if the undersides, which no one ever looks at, were to be painted. It took strenuous argument by Nissan management to persuade the workers to drop their idea.

The Japanese companies work hard to earn their devotion. Auto workers are assured of wage increases as long as the industry is profitable, and there has been no major strike in about a quarter of a century.

Workers also are assured a direct voice in determining how they do their work. If they want a robot to do the work, they get a robot. Last year, Nissan received more than 450,000 written suggestions from 57,000 employes and the authors of the best were rewarded with raises and promotions.