Tom Roberts was inspecting the "skinning line," an assembly point at the Broening Highway General Motors Corp. plant where van body frames and exterior sheet metal are joined in electromechanical fusion.

As he watched, four huge arms -- orange in color and set two apiece on either side of an automated square -- glided overhead. The square stopped. The arms descended and embraced an unpainted metal shell.

"That's the rear panel," Roberts said, urging a visitor to pay attention to the work under way in the Baltimore plant that is now a part of GM's Truck & Bus Group.

Suction-cap hands at the end of the mechanical arms lifted the shell and held it. The four-armed square moved backward, forward, then released the shell over the end of a waiting frame. There was a "kaa-chump" noise as metal met metal. And there was a smile on Roberts' face.

"I've been in this plant for 20 years. But I've never seen 'em do things like this -- never seen this kind of quality," Roberts said. "If they keep doing it this way, I think I could be around here for another 20."

That is the hope among the 3,000 production workers here, most of whom have been given a second chance to work in the domestic auto industry because of a burgeoning new segment in U.S. auto sales -- the minivan and compact van market.

GM is making small vans here. They are the Chevrolet Astro and the GMC Safari, GM's and Baltimore's entries into what auto analysts say will be a 1 million-unit, multibillion-dollar market by 1990.

GM was going to scrap the Baltimore plant, which had been turning out cars and trucks since 1935. Like many of its counterparts, it had fallen victim to deepening recession and vanishing sales.

Temporary shutdowns and permanent layoffs became a way of life at the facility. A payroll that once numbered 7,000 during peak production times in 1978 had fallen to 3,000 by last March 30, when the plant rolled out its last mid-size passenger car.

A massive GM reorganization jeopardized those remaining 3,000 jobs. The company was cutting fat, getting in shape for a hard run against foreign competitors. The Baltimore plant was old and relatively inefficient and was operated by two groups -- the Fisher Body and GM Assembly divisions -- headed for phase-out in the reorganized company.

The two GM divisions eventually disappeared. But the plant here was saved, largely because of a GM competitor -- Chrysler Corp.

While GM was mulling the possibility of shutting its Baltimore facility, Chrysler was busy building its first minivan, a vehicle that has the passenger capacity of a big station wagon, some of the cargo space of a regular van and the large exterior size and parking problems of neither.

People loved the Chrysler minivans -- the Plymouth Voyager, Dodge Caravan, and the cargo-hauler version, the Mini-Ram Van. Those models hit the U.S. market in late December 1983, rolling out of Chrysler's highly automated plant in Windsor, Ont.

At the time, the only comparable models in the U.S. market were the Toyota Motor Corp. minivan and an aging model, the Vanagon, produced by Volkswagen. But auto critics hailed Chrysler's small vans as the best of the class, largely because they were front-wheel-drive and handled with greater ease than competing models.

Toyota's presence in the domestic minivan market has been limited by quotas restricting shipments of Japanese vehicles to the United States. But the Chrysler minivans, blessed by novelty and reasonably available, became a market sensation. Chrysler has sold nearly 200,000 minivans since 1983.

Fast, high-volume sales of new products don't go unnoticed in Detroit -- or anywhere else where auto makers exist.

Industry analysts say both GM and Ford Motor Co. long had planned small vans of their own. But the two companies let Chrysler test the minivan market, some analysts say. Once it became apparent that Chrysler's $700 million minivan investment was yielding big returns, GM and Ford decided to move, analysts say.

"Chrysler did something unusual for a domestic auto maker," said James A. Mateyka, an analyst with Booz-Allen & Hamilton Inc. "The Chrysler minivan play was ahead of the Japanese, for once. The Voyager/Caravan is a winning product. It's created a whole new segment in the U.S. auto industry, and that just doesn't happen very often."

The minivan market is expanding rapidly -- from about 250,000 units sold in 1984 to 650,000 projected sales for 1985. That market will grow to more than 850,000 units by 1987, when the market is expected to become fully competitive, according to a recent report by J. D. Power & Associates, a California-based market research firm.

The small vans are money getters. For example, suggested base prices of the Chrysler minivans range from $9,147 to $10,005, but the vans often are impossible to find at those levels. GM and Ford officials in Detroit watched with admitted envy as customers trooped into Chrysler showrooms around the country to pay premiums as high as $2,000 over suggested retail prices.

GM said last March it would spend $600 million to get into the minivan market. Ford said it would spend a similar amount to bring out its Aerostar minivan later this year.

Baltimore is the only assembly site for GM's small vans, which began rolling off lines here in early November. The company so far has shipped 10,000 cargo vans. No passenger vans will be produced until GM is certain that they have "total quality," according to Baltimore plant manager Walter J. Gregonis.

"We can't afford for one of these new vans to get out with problems," said Gregonis, who conceded that passenger small-van production is running into some difficulties.

"We're producing a good van. But our biggest problem right now is getting all of our tools and equipment debugged. It's a pretty complicated procedure," Gregonis said.

A tour of the 2.9 million-square-foot Baltimore plant floor yields some examples. There are 94 painter robots and 48 others that do 96 percent of all of the body welding.

One of the computer-controlled welder robots has fallen ill on the "re-spot line," where the cage-like van frame is welded together.

"Robot's lost its welding cap," explained a worker, holding up a copper-colored cone. "No cap, no weld. No weld and the line don't move until the thing gets fixed." He laughed. "Didn't used to be that way. Before, they'd let the sucker go with a missed weld," said the worker, who declined to give his name.

That kind of shoddiness is no longer tolerable, said Roberts. "We got a lot of competition out there. We've got to build a quality product," he said. "The better the job, the longer we keep our jobs. Know what I mean?"

Workers at the Baltimore plant operate in so-called quality circles -- small groups dedicated to maintaining tools and performance in specific production areas -- in an attempt to keep quality high. Bad parts are jettisoned. In fact, largely because of new, computerized inventory procedures, bad parts tend not to find their way into the plant at all, Roberts and other GM workers said.

The union, the plant managers, city and state officials begged, cajoled and paid GM -- in the form of roadway improvements, for example -- to locate its small-van project here. "The leadership displayed" by the community "is one of the major reasons General Motors picked this plant to build the new generation of Chevrolet and GMC vans," said Donald J. Atwood, GM executive vice president.

Of the $600 million that GM spent to start its small-van program, $270 million went into retooling the old plant.

Current line speed at the Baltimore plant thus is about 26 to 30 vans an hour, 20 units under what Gregonis said would be peak hourly production. "We aren't going to speed up the line until we get everything right," Gregonis said.

Robert D. Burger, GM vice president and general manager of the company's Chevrolet Division, said that he wants Gregonis to stick to that pledge. GM expects to sell 165,000 small vans annually, Burger said. Of that amount, the company expects 75,000 "conquest sales" -- unit sales taken from competitors offering similar products.

Burger expects most GM conquest sales to come from Chrysler. "Our van is more of a van than theirs, which means that it's more versatile," Burger said.

Chrysler officials, of course, disagree. "We're selling everything that we can make," said a Chrysler spokesman, who last week said the company had only a 39-day inventory of the product. A 60-day supply is considered adequate to meet immediate customer needs in the domestic auto industry.

But Chrysler will be facing more boasts from competitors. Besides the Ford Aerostar and the Toyota and Volkswagen entries, new minivan offerings are coming from Renault, Isuzu, Mazda, Mitsubishi, and Nissan.

Also, even with extensive quality controls, there will be problems. Chrysler, for example, recently recalled 82,500 minivans to check a possible fuel-pump problem.

What you have here is a significantly new product," analyst Mateyka said. "When it was introduced, people thought the minivan basically would be a substitute for the station wagon. But it's turned out to be much more than that."

Mateyka said people are leaving sedans and other vehicles for minivans. "It's a whole new product line that's meeting a whole new market segment -- a whole new thing in the domestic auto industry."