WE SUPPOSE Mrs. Drew Lewis and Mrs.

Edwin Meese III made a mistake by signing on as volunteer extras for Ambassador Jeane Kirkpatrick's official two-week trip to Africa. They hold no official position, and their hotel and meal bills (the plane was going anyway) were going to cost the government something. Costs of another sort may flow from its being reported, in a faint but unmistakable air of tripping up the mighty, that the wives of two top Reagan administration officials are on a five- nation trip to Africa, "financed by American taxpayers," as one wire service story put it. The unspoken premise is that they are over there in Senegal, Togo, Zaire, Rwanda and Burundi larking about and abusing in some way the high positions of their spouses.

So all right: they should not have expected the government to spring for their room and board--it may not be too late for that to be remedied. It would have been better if they had been appointed to the delegation; private citizens often are. But after they have had their wrists gently slapped, they deserve something else--such as a hearty pat on the back for the service we are sure they are performing in lending their presence to the sort of "public diplomacy," representing their country abroad, that is easy to make light of but that can be extraordinarily useful all the same. We are not familiar from firsthand experience with each stop on the Kirkpatrick itinerary, but we do know that any notion that these women are lounging at the spas with the Beautiful People is palpably absurd.

It is suggested somewhat darkly that the participation of Mrs. Meese and Mrs. Lewis is inconsistent with President Reagan's austerity budget. The real inconsistency is with the work they are in a position to do. To have curious and connected spouses signing on for a goodwill mission, learning of conditions in places where not so many Americans go, and coming home to transmit their impressions around the circuit on which they travel in Washington, can be worth a heck of a lot more to the country than the cost of their room and board. Their trip entails not a scandal but a service, and they should not be having to fend off any inference to the contrary for their pains.