Wilbur Mills is knocking on doors for the Encyclopedia Brittannica.

Things aren't really that bad. The doors are in Congress. And he isn't selling the encyclopedia, exactly.He is trying to convince the appropriate members of Congress that the Federal Trade Commission is being unfair to the famous door-to-door company.

It seems Encyclopedia Brittanica is upset over an FTC order that its salesmen be forced to carry a 3-by-5 inch card which states that they in fact are soliciting the sale of encyclopedias. Similar wording is called for in EB advertising. And the salesman must show that card to a potential customer when seeking admission into a home, FTC said.

Mills, of course, needs no such card on Capital Hill. In fact, when the Senate Commerce Committee was quizzing the entire FTC about its activities -- including the Encyclopedia Britannica matter -- at some hearings a couple of weeks ago there was Mills, sitting behind the senators with their staffs.

Mill's law firm, Shea, Gould, Climenko & Casey, is one of two retained by Encyclopedia Britannica to present its case on the Hill.

EB is seeking an amendment to the FTC authorization bill that would prevent the commission from taking such action against only one firm in an without making others in that industry adhere to the same rules.

Without such a rule, the encyclopedia giant may have to stop selling encyclopedias, EB and Mills claim.

According to Hill sources, Mills and EP President Charles Swanson have been making the rounds on both sides of Congress, Pleading their case that it is unfair for the FTC to force EP salesmen to carry such cards when other door-to-door firms -- particularly encyclopedia firms -- haven't been asked to do the same.

So it was no surprise to anyone when, at the Senate hearings, Commerce Committee Chairmen Sen Howard Cannon (D-Nev.) asked FTC Chairman Michael Pertschuk about the Encyclopedia Britannica case.

For his response, Pertschuk referred to FTC Bureau of Competition Director Al Kramer, seated to his right, but only after pointing out that the FTC won the EB case in the courts, and the company is appealing the decision to the Supreme Court.

Kramer said the FTC had investigated two other major encyclopedia manufacturers for the same alleged abusive sales practices as EB, but the other firms weren't found to be using the same tactics as EB.