Geographically, Illinois' 22nd Congressional District is not Peoria. The district lies about three hours' drive south and east of that fabled provincial city. But metaphorically, this district is Peoria.

Connoisseurs of the Watergate tapes will recall that, in the jargon of Richard Nixon's White House, "Peoria" was a metaphor for the vast, flat heartland of the natiion where an immense but passive propulation of "Middle Americans," a special constituency for conservative politics, was believed to exist.

If there really is such a population, it probably lives here.

Although the 22nd is one of the biggest Congressional districts east of the Mississippi (it has slightly more land area than the state of Maryland), it contains one of the most homogeneous groupings of white, working-class voters in the country.

Census data shows that more than 98 percent of the 22nd's 464,000 residents are white, with almost all the blacks and other monority groups clustered in Danville, the district's largest city. The people tend to come from generations of native stock: in 1970, the Census Bureau found only 4 percent were immigrants or first- or second-generation Americans.

The foreign spicing in this thick domestic broth is diverse. The census listing of "mother tongues" shows that the 22nd in 1970 contained 13,283 German speakers, smaller smatterings of Frenchmen, Poles, Italians, Hispanics and Swedes, and 69 souls who answered the survey in Yiddish.

Most people here work - unemployment is lamost always below the national average - and they work, largely, in factories or on farms. By city standards, they are poor: the median family income is about $8,700 per year (as opposed to $12,358 nationwide). But $8,700 goes farther here than it does most places.

A nice house on an acre of land will rent for about $100 per month. A good, firm pair of field boots can be had for less than $35; a big stein of Gran Belt beer, on tap, goes for 35 cents in the taverns that dot the little "downtown" sections of the district's scattered cities.

The people of this rural haven take a no-nonsense approach to politics. They are wary of government handouts (except to farmers), and don't cotton to officials who want to begin new programs that will increase government spending. They generally vote Republican in national and state-wide elections, but in local races the two parties slug it out on a nearly equal basis.

The 22d district is shaped like a rough triangle, with its base running along Illinois' eastern border and the apex jutting to within 60 miles of St. Louis. It consists, for the most part, of broad, open stretches of farmland; there is not a single city big enough to earn the Census Bureau's designation of "metropolitan area."

Despite its austere features, the district boasts several spots that mapmakers consider "points of interest."

Olney, near the 22d's southern border, boasts "the only significant concentration of white squirrles in the United Staes," according to a notice in the town's tiny library. Hoopeston, at the disctict's northern edge, is the home of the nation's largest annual sweet corn festival.

Politically, the 22d has a rich history. Lincoln and Douglas debated here, and even today political debates are an important drawing card at many of the country fairs that mark midsummer in southern Illinois.

At the turn of the century, the district gave the nation a larger-than-life congressman in the person of "Uncle Joe" Cannon, who was speaker of the House office building.

Things have been considerably quieter on the congressional front for the last 20 years, during which George Shipley, a Democrat from Olney, has represented the 22d. The soft-spoken Shipley has compiled a consistently conservative voting record and a reputation as a "regular guy" among his colleagues, but have left almost no legislative mark in his 10 terms in the House.