SPRING comes late to Wisconsin, and northern farmers often wait well into April for the first robin, which heralds the start of the planting season.

A new brand of Presidential politicking has brought another harbinger of spring to the state. Long before the first robin will blow in from the South, farmers have begun to notice flocks of students moving in from Eastern colleges. They are part of Sen. Eugene McCarthy's "kiddie corps" canvassing voters for the April 2 Presidential primary.

The students offer Wisconsinites a refreshing relief from the hardened politicos who pass through the state every four years, their heads swimming with thoughts of 72 counties, ten Congressional districts, X number of delegates to the national convention. Most students descend on Wisconsin with only Rand McNally memories of the state as a cheese-colored mitten, its thumb thrust into a pale blueness labeled "Lake Michigan."

This idyllic if incomplete image is soon shattered by the realities of Wisconsin politics. "Of all fifty states of the Union," writes Theodore White in Making of the President 1960, "Wisconsin is probably that state in which professional politicians most hate to tempt a primary." It is a vast and rugged land, and in political terms, unorganized and totally unpredictable.

In 1960, pollsters predicted that John Kennedy would win nine of the state's ten Congressional districts from Hubert Humphrey. The Massachusetts Senator carried only six districts, however, with a scant 56 per cent of the popular vote.

Specters of past Presidential aspirants haunt the history of Wisconsin primaries--Sen. Arthur Vandenburg in 1940, Wendell L. Wilkie in 1944, Gen. Douglas MacArthur in 1948.

McCarthy must also realize that candidates who do manage to survive Wisconsin often die at the national conventions. This "Wisconsin whammy" has twice befallen Estes Kefauver, the choice of state Democrats in 1952 and '56, who lost the nomination both years to Adlai Stevenson.

As a political weather vane for the national election, the Wisconsin primary--pioneered by Gov. Robert La-Follette in 1903 as the first in the nation--has failed to bend even to popular hurricanes. In 1932, Wisconsin Democrats went for Al Smith, the rest of the nation for Franklin D. Roosevelt. In 1952, state Republicans chose Robert A. Taft, while everyone else liked Gen. Dwight Eisenhower.

Throughout its 120-year history as a state, Wisconsin has held an improbable rendezvous with the bizarre. It has given the world Thorsten Veblen and the Ringling brothers, Jack Lemmon and Joe McCarthy, Billy Mitchell and Frank Lloyd Wright, Edna Ferber and Harry Houdini. The state's contributions to American education include the first kindergarten and the first panty raid. It is the birthplace of the Gideon Society and the Republican Party.

The land itself is bizarre. Five times glaciers have moved down into Wisconsin, grinding and scraping and reshaping the countryside. In the north, the glaciers left behind jagged red granite cliffs and tickly-wooded hills. In the south, these hills break down into gentle kettles and morraines, the pock-mark measures of the glaciers' farthest reach.

The north is the land of Paul Bunyan, the giant lumberjack whose footprints remain as tiny wooded lakes. Wisconsinites brag that they have more lakes than Minnesota, which supposedly has ten thousand. The north is hunting and fishing country that has attracted such outdoorsmen as Pres. Eisenhower and Al Capone, and which each year draws thousands of tourists from the Chicago suburbs.

The south is dairy country--the most productive in the world. Wisconsin supplies one-seventh of America's milk, more than any other state. It also leads in the production of cheese and milk cow and heifer herds. The rich dark prairie land of the southwest corner--the "driftless area" missed by the glaciers--yields wheat, corn and hogs.

TO get an idea of the political geography of the state, it is helpful to draw a line from Chicago northward 200 miles to Green Bay, home of football's world champion Packers. Bring the line southwest 125 miles to Madison, the clean capital and university center, and then back southeast 125 miles to Chicago again.

Within this rough isosceles triangle, 80-miles in maximum width between Milwaukee and Madison, the two largest cities, 55 per cent of the state's population lives on 15 per cent of the land.

The Milwaukee-West Allis greater metropolitan area, with one-and-a-quarter million people, produces farm machinery and tractors, automobile parts and, of course, the beer that has made it famous. South of Milwaukee, in a 50-mile megopolis reaching into Illinois, are the heavy manufacturing centers of Racine and Kenosha--Wisconsin's third and fourth largest cities with close to 100,000 people each.