The Post's editorial concern {Nov. 16} about House Speaker Jim Wright's involvement in the Nicaraguan peace process discloses sound instincts but a shaky factual foundation.

No one could wish Congress or its leaders to take on diplomatic functions or otherwise to negotiate with foreign governments. The speaker contends he is not doing that, but is behaving instead as an invited "witness" to the negotiating process. The rest of us might do well to accept that characterization until it is disproved by competent evidence.

There are at least three reasons why a qualified legislative "witness" is not only appropriate but necessary to the current state of play in Central America.

First, Congress must decide in January what, if any, further military aid to provide the contras, and it will need for that purpose to make a soundly informed judgment about the status of peace talks. Second, unfortunately, the current executive has been shown by the Iran-contra hearings to be an unreliable witness on these matters. Third, this executive's own involvement in Central American negotiations has in the past had as its constant theme and purpose the scuttling of any peace process -- so that there is a disqualifying conflict of functions and interests between the White House as participant and the White House as witness.

The speaker may not be entirely free from bias, of course, or from possible overreaching, but there are ways to cure and govern that. Let Mr. Wright keep a confidential written summary of his "witnessings" and make it available for private examination by the president, Cabinet heads and members of Congress from both parties in the days immediately preceding the next contra aid vote. Or if Minority Leader Robert Michel wants to make a constructive contribution, let him join with the speaker in these "witnessings," subject to a comparable pledge of confidentiality.

That could help also to limit the "appearances" problem and to curtail the precedent set by these extraordinary arrangements. The next administration, to be elected a year from now, will presumably choose to return to leveling with the people's representatives, so that we can all get back to a more straightforward separation of powers. ROLAND S. HOMET JR. Washington

The editorial "What Is Jim Wright Doing?" provides a shallow and misleading conclusion to the question it asks.

Having been invited by President Reagan to participate in the formulation of this delicate foreign policy question, Mr. Wright, it seems to me, has an extraordinary responsibility independently to inform himself of the intricacies of the negotiations.

For the speaker of the House to rely on second-hand information from a petulant and contrite administration would be an abrogation of his duty to his congressional colleagues and to the public. CLARENCE J. MARTIN Alexandria