Thirty years ago this manufacturing city was a model for a classic academic study of the American middle class. Last week it attained distinction of a different sort: an unemployment rate of 19.1 percent, highest in the United States.

Almost twice as dependent on manufacturing jobs as the average American community, Illinois' second-largest city builds car parts, hardware and machine tools, products that do not sell during a recession.

Today, almost one worker in five is unemployed in this heavily Swedish and Italian city 86 miles northwest of Chicago. It is devastating for many men like Melvin D. Shook, interviewed as he waited in a local unemployment office.

"I've never been laid off in my life," he said. "I didn't know what it was. I've worked 8, 12, 18 hours a day since I was 12 years old."

But there is more than unemployment to the story of this city, which 30 years ago partly inspired Prof. W. Lloyd Warner's book, "Social Class in America." With a population of 280,000, Rockford exhibits the paradoxes that characterize unemployment everywhere in America.

The city still shimmers on the surface with midwestern contentment like the Rock River. The city has initiated a five-year, $47 million downtown redevelopment project, and more people than ever are playing golf on the city links.

But, at the same time, some of the jobless are exhausting unemployment benefits and face the loss of their houses.

Rockford's plight reflects that of many Great Lakes cities suffering from dwindling jobs and opportunities as manufacturers move south.

Of the 14 American cities with unemployment rates higher than 15 percent, according to U.S Department of Labor statistics for June issued last week, 10 are in states bordering the Great Lakes. Meanwhile, employment grew in Florida and Texas.

More than 42 percent of Rockford's labor force works in manufacturing, compared with 23 percent nationally.

Manufacturing concentrates on the automotive, hardware and machine tools industries. The machine tools industry is what economists call a lagging indicator, responding late in the economic cycle to downturns as well as upturns.

Past slumps have not lasted long enough to hit machine tools, so past recessions have not been so bad for Rockford.

But early this year even machine tool companies started closing doors and sending workers home. A few days ago, the president of Rockford Machine Tool Co. announced his company will close, adding 113 more workers to the unemployment rolls.

In the 1950s and '60s the city boomed, but reached its peak in manufacturing employment in 1968 and since then has suffered cycles in which this is by far the lowest trough.

Rockford has suffered from the general shift in manufacturing to the Sun Belt, and local officials say it may be out of equilibrium, with more manufacturing workers than it can support even in good times.

In economic theory, when a community is out of equilibrium people leave to look for better prospects elsewhere. That is happening to some extent but at a considerable human cost.

"No Applications Accepted" signs have blossomed, undermining the hopes of the streams of unemployed who scrimp for gasoline to roam from rejection to rejection. Some talk wistfully of moving to the Sun Belt and a few have loaded children and possessions onto trucks in a small-scale reenactment of the migrations during the Depression.

People like to talk about the opportunities elsewhere.

"I hear there are lots of jobs in Colorado. A lot of the places have 'Help Wanted' signs," said Sue Hibbs, who graduated from high school in June and was laid off two weeks ago from her factory job. Many of her friends have left for Colorado or California or Texas, she said, and since she cannot afford college she probably will join them.

But older people find it harder to leave, especially since almost two-thirds of families in Rockford own houses.

When a worker is laid off, the family depends on a spouse's salary, unemployment benefits or savings many have amassed by thrifty budgeting over the years.

Partly because of savings, and the reluctance of local people to borrow much money, foreclosures have risen only a little from a a year ago, according to bank officials. The banks are also helping some people refinance loans.

In desperation, some turn to welfare. The number of unemployed receiving aid to families with dependent children has almost doubled from one year ago.

Many others must be rejected because they own too much property, such as a second car, even though they protest they cannot eat their property. So they try to sell what they own even though there are no buyers.

More than 500 families have turned to the Salvation Army for food, clothing or shoes. The Salvation Army provided food to 55 percent more families from April to July of this year than in the same period last year, according to city coordinator Alvin R. Nelson.

The worst often is psychological. Officials say the impact has been particularly devastating for middle-aged men who worked in factories and prospered, and bought homes and cars only to find themselves out of a job and without prospects of finding another.

"We're having repeated cases of men -- women too, but especially men -- where they're breaking down in the intake center, crying or swearing, because they have to come to our office," said Scherri Hall, administrator of the Winnebago County department of public aid.

"There is more wife abuse and child abuse, more alcoholism and severe depression, which is affecting the children; they run away," Hall said.

Calls to a local suicide hotline are up, although suicides are not on the increase.

But even those waiting in unemployment lines tend to say they will wait and see if the economy improves before blaming President Reagan for their problems.

"Reagan ain't no worse than anybody else," said Leon Taylor, a contractor who has lost two trucks and his house because he could not make payments. "He's just got a different way of doing things."

Added Joseph Utzig, laid off from the nearby Chrysler plant after 16 years there, "Give the man a chance. He's the only man brave enough to try it. It's not his fault, but you kind of get blamed for it.