THE ELECTION returns from Illinois have been a shock. While most of the political pundits were focused on the Chicago races for aldermen and on challenges to four members of Congress, the primaries for state-wide office resulted in the nomination of two unknown followers of the political extremist, Lyndon LaRouche. Democrats chose Adlai Stevenson III as their candidate for governor but rejected two others who had been fielded by party regulars for the lieutnant governor and secretary of state races. How could this have happened?

The LaRouche candidates, Mark Fairchild, 28, and Janice Hart, 31, were apparently not thought to be a threat to party regulars, and little attention was paid to their backgrounds or their campaigns. It is difficult -- and unsettling -- to believe that voters consciously chose them for their views, which Mr. Stevenson described as "extremist philosophy steeped in violence and bigotry." We along with droves of others prefer to believe that something else went wrong, that voters did not realize who these candidates were, that they made a mistake because they did not have enough information, not because they approve of Lyndon LaRouche's poisonous views.

Mr. Stevenson's position is excruciating. His unwelcome and embarrassing running mates cannot be removed from the ticket, and his remaining choices are unpleasant. He can campaign with a pledge to abolish their offices if elected; he can form an entire new party and field a whole new slate for state-wide office, none of whom can be current Democratic nominees; or he can, as one newspaper has already suggested, withdraw from the race and endorse his Republican opponent, Gov. James Thompson.

In other states, candidates seeking to avoid this humiliating fate have been scrupulously examining the credentials of minor, supposedly harmless opponents searching out LaRouche followers. Democratic National Committee Chairman Paul Kirk has called on party officials in all states to check carefully for such candidates. Two in Maryland are seeking the Democratic nomination for govenor and senator. Another has turned up in California as the sole entry in the Democratic primary for a Republican-held House seat.

The Democratic Party, the press and the voters who now claim to have been hideously surprised all bear some responsibility for what happened, if what we are talking about here really is, as we devoutly hope, a failure of information. If it turns out that such candidates continue to win even when voters realize who they are and what they stand for, this country is in much bigger trouble than the returns from Illinois seem to signify at the moment.