THIRD-PARTY or independent candidates have almost always followed a comfortably predictable pattern in American politics. First, these movements have originated quite some distance from the political center, usually on the left, and have been charged with an ideological fervor and intensity. Second, they have drawn their voter support principally from the party from which the candidate came. It was the Republican Party, for instance, that Theodore Roosevelt hurt when he ran as a Bull Mooser in 1912 (finishing second in the national vote) and received credit, or blame, for having put a Democrat, Woodrow Wilson, in the White House.

Election year 1980 insists once again on being different with respect to at least one independent presidential candidate, the recently announced Rep. John Anderson of Illinois.

Mr. Anderson, a non-winner in six Republican primaries this year, has caused much more alarm in President Carter's camp than in that of Ronald Reagan, the two front-runners for their parties' nominations. The Carter campaign's lawyers are already preparing their arguments to help keep Mr. Anderson off as many state ballots as possible. John White, the president's national party chairman, has publicly branded the Anderson effort "a fool's errand." Mr. White's fellow Texas and fellow supporter of the president, former ambassador Robert Strauss, predicts semi-confidently that the Anderson candidacy will eventually become only a temporary "parking space" for some voters on their inevitable route to the Carter column.

And public opinion polls seem to confirm, for the present, the concern of President Carter and his lieutenants. The generally reliable Iowa Poll now has Mr. Anderson drawing 21 percent of the vote in a three-man race. Mr. Reagan leads President Carter in the same survey (with Mr. Anderson in) by 35 to 32 percent. Without Mr. Anderson listed, the president holds a one-point lead over Mr. Reagan. So the tradition of the independent hurting his party of origin most does not appear to be holding thus far in 1980.

The other aberration of the Anderson candidacy is that it is not fired by an ideological imperative. If anything, it is a movement from the ideological center. Mr. Anderson can probably be most accurately described as someone who is "liberal" on the cultural or social issues and rather conservative on fiscal issues. His present support, again according to public opinion surveys, is more generational and occupational than ideological. Anderson voters are more likely than not to be college-educated, under the age of 35, affluent and probably fiscally conservative and culturally "liberal."

As the candidate and his allies go about the exceedingly difficult job of qualifying for seperate ballot listing, perhaps we will learn whether independent candidacies have failed in the past because they have come from a too-narrow ideological base, and if the "middle" is simply a lonely political place or a point from which to build a real national effort.