THE SENATE Foreign Relations Committee is about to report out the nomination of Alexander M. Haig Jr. to be secretary of state and, like almost everyone else, we see no good reason why it should not. By his experience and in his comments on the substance of a secretary's responsibilities, Gen. Haig has surely shown himself to be qualified.

True, the committee's hearings have not resolved the questions of judgment and character that his service in the Nixon White House had raised in some people's minds. But Gen. Haig and, for that matter, the Senate's Republicans are not responsible for that. It would be unfair to penalize him or the incoming administration by holding the nomination hostage to the Senate's access to materials that would likely be slow in coming in the best of circumstances and that, if they did come, might or might not bear on the questions that trail after Gen. Haig.

The regrettable fact is that if Gen. Haig is confirmed, as he no doubt will be, he will take office under a cloud a good deal bigger than a man's hand. It is not irrelevant that the hand is that of former president Richard M. Nixon. It was Mr. Nixon whom Gen. Haig was serving when he performed the acts that stirred the doubts about him lingering still. It is Mr. Nixon who now declines to take the single simple step that, Gen. Haig contends, would show skeptics there is no foundation to those doubts.

That step is, of course, to release the tapes (and before that the logs) of 100 Nixon-Haig conversations in 1973. Gen. Haig has invited the Senate to solicit those tapes. The administration did its part. The Foreign Relations Committee agreed after a bit of Democratic pulling and Republican hauling on a reasonable set of terms on which the committee would seek them. But Mr. Nixon says no.

We know that the tapes are tightly bound in historical precedents and legal procedures and that Mr. Nixon has a right to try to control access to them. It is grotesque, however, that he should be asserting this right in a way that prevents the Senate from doing its constitutional duty as it best sees fit.

That result does more than frustrate the Senate. It denies Mr. Reagan the comfort of having a secretary of state without an asterisk on him. Perhaps most important, it keeps Mr. Reagan's prospective chief Cabinet officer dangling, however lightly, on the end of Mr. Nixon's string. How can the former president not wish to spare his erstwhile associate the burden of conducting his office under the suspicions that flow unavoidably from that arrangement?