IT IS A refreshing note of trust and straightforwardness Secretary of State Cyrus Vance has struck by ordering that no conversation in his department be monitored without the "express consent of all persons involved" - unless he or his deputy grants an exception in advance. And we are pleased that the President has decided to follow suit in the White House. This will not restrict the often routine and useful practice, one not unknown outside government, of having a record made of certain conversations, whether these take place on the telephone or in someone's office. But it should help restore a good measure of the confidence lost by disclosures that in past administrations (a) many conversations were taped or recorded without the awareness of all people involved, and (b) that on some occasions national security officials had their calls secretly monitored with the knowledge of their superiors, if not at their instigation. This is one aspect of the management of foreign affairs in recent years in which continuity is of no merit at all.

Now, your typical diplomat, American or foreign, probably figures that all of his conversations, on or off the phone, are being monitored anyway, and so speaks with discretion and precision to match.It is not so much paranoia as professionalism that underlies that sort of caution. Journalists dealing in national security affairs often proceed in the same way. Indeed, occasions can arise in which diplomats or others want the conversation to be recorded, so that there will be no question later of what was said. So we doubt that the diplomatic community is going to change its style on account of Mr. Vance's new order. That does not, however, deprive it of value. That value is symbolic but also real. It announces a manner of open dealing - not necessarily public but open. In a word, it announces civility and rectitude.

Mr. Vance did not describe the basis on which he or his deputy might approve the monitoring without notice of certain conversations. One might guess that the exceptions would involve special diplomatic or security leak situations. It could only serve what we take to be the Secretary's own purpose if he were to spell out his standards and thereby obviate speculation about the size and nature of the loopholes he has left. Meanwhile, we hope that his example - and the President's emulation of it - will be contagious throughout the government.