AT THE AGE of 58 and after 20 relatively unpublicized years in the House of Representatives, John Anderson seems to have become a full-fledged folk hero and a major force in the presidential politics of 1980. Three separate items confirm this heady status for the man who is said to have a chance to win his first primary in his home state tomorrow.

The first report of success may be found at the Federal Elections Commission. The Anderson file shows that the campaign is raising money at a breakneck clip. Nine months were required to raise the first million dollars; the second million will have been raised in less than three weeks. Response to the campaign's direct-mail appeals is bringing in more than $55,000 a day, in donations averaging about $40 each. Since every individual contribution, up to $250, is matched by federal funds, the daily take is probably better than $100,000, just through direct mail.

Mr. Anderson was one of the principal sponsors of the election reform act, which was intended, among other things, to diminish the importance of money in politics. Interesting: now no candidate is considered "serious" until he can qualify for the matching funds provided under the act. And the first sign that a candidate is in trouble at the polls is his being overdrawn at the bank. John Anderson is anything but overdrawn right now. So he is very "serious."

The second indication was the appearance of the candidate on "Saturday Night Live" and in the comic strip "Doonesbury." No evidence beyond ratification by these two cultural arbiters was required to show that Mr. Anderson deserved a second look.

But by far the most significant fact is the recurring story about a possible third-party run in November by John Anderson. He has described the legal and logistical problems of such a project. Under pressure from his primary opponents, in particular George Bush, Mr. Anderson has stated categorically that he will not support Sen. Edward Kennedy next November and turns away any third-party speculation, for the time being, with a confident and unconventional prediction: "I'm going to be the Republican nominee." But with the nominations of President Carter and Ronald Reagan becoming more likely each passing Tuesday, there could very well be a constituency for a third-party effort headed by Mr. Anderson or somebody else.

In a Carter-Reagan contest, the present betting would certainly be that Mr. Anderson would take more votes from the Democrat than from the Republican. It may tell us a lot about the confused state of our politics or it may simply reveal the philosophical origins of his candidacy that Mr. Anderson, on a third-party ticket, would doubtless hurt Mr. Carter more than he would hurt Mr. Reagan and the party that rejected his bid.