The skeletons of Chevrolet Monte Carlos sit silently on the conveyor belt at General Motor's Broening Highway plant here.

Across the harbor, steel shipments from Bethlehem Steel's giant Sparrows Point plant last year reached their lowest point since 1946.

But just a few miles away in the industrial park adjacent to the Baltimore - Washington International Airport, business is booming at the Westinghouse Defense and Electronics Systems Center.

And in the high-technology corridor of Gaithersburg, business is flourishing for Digital Communications Corp.

The pattern of Maryland industry is the pattern of the country.

Maryland, which houses more than 80 percent of the 451 standard industrial classifications of businesses, boasts that it is a microcosm of the nation. Although it enjoys many of the benefits of that diversity, such as jobs for different kinds of workers, it also suffers some of the setbacks that beset the whole nation -- such as declining employment in the steel, auto and related industries.

The GM plant is like many other auto assembly operations around the country. Production is down because people aren't buying cars. And although every 40 minutes at Bethlehem Steel here golden iron gushes into a burst of sparks that rival any fireworks display, that plant is producing steel below its capacity and isn't faring any better than steel mills across the country.

But many declinning industires in the state have just had to suffer -- and no help appears to be on the way. The state can't afford to prop up the industries. Besides, despite the failure of some firms, other companies -- particularly in high technology and communications -- are gowwing. cAlthough thousands of manufacturing jobs have been lost in various industries over the years, those losses have been offset by gains in other areas, according to Maryland Economic and Community Developent Secretary James O. Roberson.

"We're going to see growth in manufacturing, just in different industries" such as high technology, Roberson said. "We're now the world leader in communications," with firms such as Communication Satellite Corp. and Digital Communications located in the state.

"I'm not pessimistic" about the future of some industires, Roberson said. "But it will be a painful adjustment." Bethlehem Steel is "the most modern tidewater mill in the world," Roberson said. But that doesn't do much good when there's no demand for the product, especially by the auto industry. Helping Bethlehem Steel "won't do much good, not unless we can teach General Motors to compete with Datsun," Roberson said.

"It's going to take an awful lot of high-technology industries to take over the jobs if this place shuts down," said William G. Groben, assistant manager of Bethlehem Steel's Sparrows Point plant. "It takes a lot of industry to generate roughly 19,000 to 20,000 jobs."

In addition, the Mack Truck plant in Hagerstown has had to lay off employes, Roberson noted. At one time it employed between 1,200 and 1,500. Now there are 600 workers there, Roberson said. The Kelly Springfield tire plant in Cumberland also is suffering, he added.

Fairchild Industires and Westinghouse, two giants in the defense contracting business, are faring well and so is Black & Decker, which makes many do-it-yourself tools, Roberson said. Industrial toolmaking, however, has been weak, he said.

During a visit to the GM assembly plant earlier this month, only the truck assembly was in operation after 1,900 workers had been placed on temporary layoff. Automobile production based on demand had dropped from 248,502 in 1973 to 133,517 last year. Truck production, which peaked in 1978 at 118,311 dropped to 87,072 last year. t

Ironically, while the auto industry is suffering -- partly because of sharply rising oil prices charged by Middle East oil barons -- among the Baltimore plant's best sellers are pickups, loaded with every option imaginable, which are exported to Middle East moguls. Workers sometimes take naps in them while waiting for their shifts to begin.

Until last year, the Baltimore assembly plant was faring better than others in the industry, said Nelson Lawhon, the plant's spokesman. During the 1979, the itermediate-sized cars produced here were still in demand by consumers, Lawhon said, and Baltimore Harbor made it convenient for shipping trucks overseas. However, "This past year we've been in line with everybody else," Lawhon said. "We've taken our licks like everybody else.

"It's tough times. That's all there is to it," he said.

In 1978, the plant employed 7,090 employes. On Feb. 1 the plant had 2,700 persons working with 2,000 on indefinite layoff and 1,900 temporarily laid off. pThe payroll as recently as 1979 had climbed to $138.0 million compared with $39.1 million in 1965. Last year the payroll has dropped to $103.9 million.

But there is hope, Lawhon said. General Motors last year decided to retool, modernize and expand the 47-year-old plant to make 1983-model front-wheel-drive cars, but Lawhon said he didn't know yet what kind of cars they will be. The new assembly equipment will allow the plant to convert more easly to differnt sizes of vehicles in the event of another recession.

The Sparrows Point Bethlehem Steel plant is twice as old as the GM assembly facility, and it's impact on the Maryland economy is probably twice as great. Last year the plant, located on 2,500 acres, had a payroll of $500 million and bought $200 million in supplies from other companies in the state. Thestate's largest private employer Bethlehem Steel also paid $19 million in the state and local taxes, Groben said.

But Bethlehem Steel is operating at 69 percent of its capability. This year, Groben said he expects "a modest increase" in production. The plant produces steel used in appliances, cans, construction and shipbuilding products, automobiles, barrel drums, bolts, screws, rods and cable strands.

"The level of profit that we have been experiencing today will not support the capital outlays that we'd like," Groben said. The plant's peak of production was in the late 1950s and early 1960s, he said. "Our shipments in mid-1980 dropped to their lowest level sine 1946."

Ten years ago the company reduced its production capacity from 9 million ingot tons of steel to 7 million tons when its orders fell off and one facility was shut down, Groben said. Since 1971 Production has fluctuated greatly," he said.

In the early 1970s, the work force at the Sparrows Point plant was about 25,000. During the 1980s the normal work 25,000. During the 1980s the normal work force should be about 18,500, Groben said. Now 2,200 of the 18,500 workers are laid off.

"If business conditions change and we see increases in demand or steel, those people will be brought back," Groben said.

Washington Defense and Electronic Systems Center near Baltimore-Washington International airport is a different case. It is near the top of one of the fastest-growing industries in the country -- high technology and defense. The defense center employs about 14,000 people in Maryland and has openings for dozens more.

"What is occurring is a change in the composition of our work force, not shrinkage," Harry B. Smith, defense center president said recently. "For example, we now have openings for more than 200 engineers and other technical personnel, and we expect this requirement to grow as our airport complex continues to move toward a higher-technological orientation."

"The defense center is experiencing record sales and production backlogs," Smith continued. "A more favorable public attitude toward defense should allow these business levels to continue, provided Westinghouse maintains its competitive edge."

Last December the company anounced a $100 million, five-year expansion and modernization program at the airport complex.

"Competitive threat to our leadership position in airborne and surface electronic systems, both in this country and abroad, has never been more clear," Smith said. "We believe this investment will equip us to remain at the forefront in electronic systems design, development and production."

The defense center has an economic impact on the area annually of about $2 billion, the company said.

Whenever a telephone call is made overseas, part of the equipment used to transmit the message probably comes from Digigal Communications Corp. in Gaithersburg, one of the nation's fastest-growing high-technology firms.

The company began in 1971 with President O. Gene Gabbard, along with "a secretary and a Xerox machine in a 120-square-foot office in Rockville," Gabbard said. Ten years later, Digital has nearly 600 employees most of whom work in an $8 million glass-and-brick complex on 51 acres in Gaithersburg.

While some firms in Maryland are laying off workers, Digital's employes are working designing, building and testing digital telecommunications equipment and systems, including satellite earth sations. The firm already has a backlog of orders for 200 earth satellite stations to carry information across the country, Gabbard said.

The first year the firm did $500,000 in business. Last year it did $40 million in business.

During the firm's first quarter, ended last December the firm had new orders of $23 million, Gabbard said. As he toured the spacious, clean and quiet assembly lines, which contrasted markedly with the state's heavier, declining industries, Gabbard said business can only go up. "We do expect to continue our substantial growth," he said.