JOSEPH L. RAUH JR., our friend and indefatigably faithful correspondent over the years, has written us a not-so-friendly letter about faithless convention delegates. In his letter, which appears on this page today, Mr. Rauh, a Kennedy supporter, takes issue with our recent charge that the moralizing pursuers of "freedom" for all the (mostly Carter) delegates on the first ballot in New York were up to their hip boots in hypocrisy. He suggests that we could only have been motivated to take this shocking position by a case of "Carter tilt." Mr. Rauh acknowledges that delegates do have some responsibility to that candidate whose resources and good name they used to get to the convention. But he aruges that delegates may legitimately support someone other than that presidential candidate if "there has been a change in circumstances since the primary or caucus where they were selected."

And where hasn't there been a change of circumstances? Primaries and caucuses themselves change some circumstances. And we freely concede that we cannot come up with a single primary or caucus that was not held under significantly different circumstances from those that now obtain, even the most recent primaries and caucuses. But we cannot buy this Loophole of Changed Circumstances: it is an expedient that was thought up to further Sen. Kennedy's candidacy -- and the reforms it would overturn be damned.

We will call a surprise witness here: Sen. Kennedy himself before he was in the particular Changed Circumstance he finds himself in at this point in his own 1980 presidential campaign. He was quoted in The Boston Globe of May 23, 1976, in response to a question about whether the 1976 Democratic convention could deny the presidential nomination to a candidate who arrived on the floor with some 1,350 of the 1,505 delegates then needed for nomination. oSuch a candidate, Sen. Kennedy answered, "would have demonstrated sufficiently broad appeal to justify the nomination. I think if a political party denies such a person the nomination, I'd think it would be a real distortion of the expressed will of the working members of the Democratic Party."

We agree wholeheartedly with the Kennedy position -- and will leave it to Mr. Reagan to judge what that may mean tiltwise.