Ambassador-at-large Vernon Walters' recent secret mission to Buenos Aires was, in the language of government, "to facilitate the future." In the language of people, that means worrying about what happens after the Falklands crisis.

"How do you worry about the future?" said Walters the other night at the Moroccan Embassy, repeating the question posed by reporters crowding around him. "Well, you have a war and eventually you come back to peace, and you have to get along with people when it's over."

By way of example, Walters, who has made a lifetime career out of secret governmental assignments and who is now special assistant to Secretary of State Alexander Haig, told of recently rereading diaries he kept during World War II. When he reads them now, he said, he finds that he thinks differently about Germans today than he did during that time.

Talking about the need for integrity when one is on a mission, he said, "If I didn't have lots I wouldn't be on it . . . You know, hanging in my office at the CIA was a picture of my home and garden in Florida. When I put it there people said, 'What is it?' And I said 'That's what's waiting for me.' The day I'm asked to do something I disapprove of or I think is wrong, I won't do it."