AS FAR AS WE CAN understand it, Ralph Nader's main criticism of his former colleague Joan Claybrook, now the head of the National Highway Traffic Safety Administration, is that she operates differently as a public servant, working for all the people, from the way she did as a private crusader for consumer interests. In calling for Miss Claybrook's resignation earlier this week, and suggesting that she return "to the citizens' movement" to "instruct active citizens on how to avoid pitfalls before they take government posts," Mr. Nader warned that if she didn't resign, her "professional ethics" would be open to question. Mr. Nader apparently believes that his former associate has sold out - that (he wrote in a column three weeks ago) she "may be on her way to becoming Henry Ford's friend."

As traffic is temporarily halted by Mr. Nader's latest recall effort, the issue is not whose side one is on but that both parties are being emphatically true to form. Miss Claybrook is not the first activist to go into government and learn that decision-making "on the inside" is no longer a merry romp in the lush garden of simplicities: good guys against bad guys, truth against lies, our virtue against their evil. Nor is Mr. Nader the first crusader to be imbittered by the thought that one of the true believers is backsliding from the faith.

But after saying that the roles of both parties are being performed much as expected, we have to add that only the naive would have thought eight months ago that no limitations would be placed on Miss Claybrook in her new job. As for her performance, in that we think it is absurdly early to offer a final judgment. More disturbing, it is reckless of Mr. Nader to suggest to Miss Claybrook that "underneath your inhibitions is the fear of squarely confronting the behavior of the Secretary's office." How does he know what Miss Claybrook is afraid of? Is he the all-knowing judge of other people's inhibitions? Even on the issue of her record, a spokesman for the insurance Institute for Highway Safety - a group known for its dogged research into auto-safety matters - says that Miss Claybrook "has been very effective."

We don't think that Miss Claybrook ought to resign from her job. Nor should Mr. Nader resign from his. The latter has a 12-year record of often useful and constructive advocacy. He believes "the most important status in democracy is that of the full-time citizen." Exactly what full citizenship has to do with throwing mud at federal officials - saying this week that Miss Claybrook is afraid of her boss, saying three weeks ago that she has lost control of her conscience - isn't clear. Or may be it is so clear as to be starlingly obvious: It has nothing to do with it.