We left ''July 1969 A.D.'' intact because it was a shrewd way of sneaking God in: the use of the initials for anno Domini, ''in the year of our Lord,'' would tell space travelers eons hence that earthlings in 1969 had a religious bent; piously, we made sure that a Bible with both Testaments was included in the spacecraft's cargo.

What should the President say to the astronauts in his phone call to the moon? Frank Borman, our liaison with the astronauts, brought the image-making up short with, ''You want to be thinking of some alternative posture for the President in the event of mishaps.'' To blank looks at this technojargon, he added, ''like what to do for the widows.'' Suddenly we were faced with the dark side of the moon planning. Death, if it came, would not come in a terrible blaze of glory; the greatest danger was that the two astronauts, once on the moon, would not be able to return to the command module.

In that event, with no rescue possible, the men would have to bid the world farewell and ''close down communication'' preparatory to suicide or starvation. It would hardly advance the cause of space exploration to force a half-billion viewers and listeners to participate in the agony of their demise. I prepared an appropriate statement about men who came in peace and stayed to rest in peace, holding it in my desk drawer in case of tragedy.

What none of us expected was editorial flak about the newly elected President signing the plaque and congratulating astronauts over the phone on behalf of all Americans. We underestimated the resentment of Kennedy partisans; Presidents Kennedy and Johnson launched and encouraged the space program, grumped The New York Times, and it was ''unworthy'' for President Nixon to ''share the stage'' with the astronauts merely because he was in the White House ''by accident of the calendar'' at its fruition. The Washington Post added that Nixon should not have signed the plaque because the moon shot was no ordinary public works project.

The President ignored this not only because he enjoyed offending these editorialists but because he planned to use the American space triumph to override the public preoccupation with Vietnam. He would follow his trip to the splashdown in the Far Pacific by a return through Europe, where he would plot with Rumania's Ceausescu about an approach to China.