Like thousands of other troubled Chicagoans, Katie the Bird Lady, Nguyen Trung the Vietnamese Survivor and Ladora Raczy the Widow have prepared for Thanksgiving the only way they know: with food from the soup kitchens and shelters of a city seeing rising numbers of the jobless, the hungry and the homeless.

As never since the Great Depression five decades ago, Chicago is being challenged by harsh, unexpected truths of unemployment, manufacturing recession and the ills of the nation's Rust Belt.

Almost any time of day, now, lines of poorly clad people can be seen gathering quietly outside the soup kitchens and church basements, waiting for handouts of food. Welfare officials say the increase in demand, especially since the weather turned cold last month, has been extraordinary.

According to a city task force on hunger set up by Mayor Harold Washington, "887,929 persons . . . are at risk of hunger in Chicago. This number equals 29.5 percent of the city's total population of 3 million , or more than one of every four Chicagoans."

"The hunger problem is much more serious than . . . anticipated. It is shocking, frightening and inhumane. How can the richest country on earth allow this to happen to its people?"

Unemployment here is 9 percent, higher than national figures. Thousands of factory jobs that disappeared during the recession will never return. While glamorous, new condominiums rise along the lakeshore, age, vandalism and daily calamities such as fire or dispossession have cut into the housing stock.

The mayor told a congressional subcommittee this year that as many as 25,000 Chicagoans "exist like the Untouchables of Calcutta, sleeping in the streets and alleys and abandoned autos . . . an indictment of us as a people."

The number of public and private food banks has tripled in the past three years, according to Leslie Jacobs of the mayor's task force. There seems to be no sign that the trend is temporary. In 1982, the city distributed 1,000 boxes of canned goods a month. The monthly total is now 20,000 boxes, and demand is rising.

"Emergency food is temporary," Jacobs said. "It is not meant to be permanent. But it is turning into a main source of food."

Recent surveys indicate widespread health problems related to hunger. Admissions to Cook County Hospital for symptoms of malnutrition have increased 24 percent since last year. The hospital also reported 223 new cases of pulmonary tuberculosis in 1983, a 32 percent increase of a disease associated with hunger. Infant mortality here is about 60 percent higher than the national average, officials said, a statistic showing the effects of chronic undernourishment.

In all, more than 400 pantries, soup kitchens and shelters are operating in the city. Most are located outside the Loop, in depressed neighborhoods of traditional, frame "two-flat" duplex houses among factories and warehouses that have long since shut their doors.

In the ethnic enclaves beyond the financial and commercial district, life's threadbare circumstances cannot be avoided. One is the area around St. Thomas of Canterbury Roman Catholic Church on the North Side. This is a neighborhood of overlapping ethnic groups, where Vietnamese, Guatemalans, Laotians, Mexicans and Puerto Ricans live.

In June, the church pantry's volunteers and paid staff served meals to 900 persons twice a week on a regular basis, according to assistant director Michael Cormack. By September, they were serving 1,000. Now, the number is 1,300, a steady stream of needy families, single persons, disabled and elderly.

The pantry's packages for monthly food distribution contain canned goods, evaporated milk, cereals, honey, dried milk, butter and other staples donated by local corporations and residents, or from federal and local public assistance programs.

Richard Knopp said the number of people dependent upon the pantry has risen fivefold in the five years he has been associated with the parish's food program.

Among those who stopped by recently were Mrs. Raczy, whose husband died in October. She rents two rooms in a small hotel nearby, paying $220 a month of her $314 monthly widow's stipend, her sole income. In the past decade "I've had four mental breakdowns," she said. Unable to work, she finds it difficult to get by on her income and federal food stamp assistance.

Nguyen Trung, who arrived in the United States in 1980 after escaping from South Vietnam, was at the church seeking help with forms and applications for various assistance programs. He speaks almost no English and life has been without much reward during his years here.

The one bright spot in the pantry was Katie the Bird Lady, a diminutive, 79-year-old bundled in an assortment of coats and dresses. She had dropped by to pick up stale bread for the park pigeons she feeds. She burbled about her birds in an unintelligible tongue.

"She lives somewhere on Clark. She seems like a happy-go-lucky person, my little bird lady. She's got names for lots of the birds, been coming here for years," Knopp said.

More than half the pantry's visitors have "mental illness," Knopp said. "Twenty percent don't have a place to live, they're just street people. With the mental problems, you can help them, but you find them right back on the street. A lot of them are drinkers, alcoholics. But to me, they're still human beings. They need something to eat, just like anyone else."