A funny thing happened on the way to D-Day: memories of the staff that drew up the plans

Once it was in my power to set the history of Europe back a hundred years. Or so I was told by a very military gentleman, an officer in one of His Majesty's Guard Regiments. That was in the 1940s, and no such opportunity has crossed my path since. I hope it never will.

The officer in question was interviewing a group of women soldiers (all of us drafted) to work with the D-Day planners. And since our work would mean that we would have to know the time and place of D-Day, he intended to terrify us into complete secrecy. He succeeded.

He was just the man to do it. Very tall, very military, he wore one of those hats with brims that slant down over the eyes, forcing the wearer to throw his head back in a haughty fashion. (''How can you see, sir?'' ''See. . . ? You aren't meant to see, Corporal Marsh.'')

Now that we know Hitler didn't win, it's hard to turn the calendar back 40 years and remember how awesome it was just to consider invading Europe - ''Fortress Europe.'' But somehow it's the trivial side of secret-keeping that keeps popping into my mind.

There was the Wren (member of the Women's Royal Naval Service) who was typing in front of an open window when a sudden breeze caught her carbon paper and dropped it in St. James's Square below. Any German spy who happened to be passing by and had a mirror handy could, I suppose, have arranged for a whole convoy of ships to be sunk. But then he would have had to race a panic-stricken Wren who dashed out to retrieve it.

Then there was the woman living across the square who wanted to know if it mattered that she could look into our offices and at dusk when we turned on the lights could read the maps of coastal France on our wall with all the red pins in place. They looked important, she thought, and perhaps they were secret. They were.

When the invasion plan was still a wrinkle on the planners' brows, someone in charge of code words assigned to it the next name on the code list - ''Mespot.'' It seemed like a good, secure word - surely no spy would connect that with the invasion of France. But Winston Churchill didn't like it. It had no ring to it - no rallying sound about it. So it was changed to the more dramatic ''Overlord.''

We who had been working for Intelligence for a few long weeks considered this terribly amateurish of him, but had to agree that ''Operation Mespot'' wouldn't have sounded well in the history books. And so typists were up all night changing the name in all the documents.

Actually we did more than type. We had full use of rubber stamps marked ''Secret'' and ''Top Secret'' and could use red sealing wax to seal envelopes carrying devastatingly important documents. I learned a lot in those days: how, for instance, to turn tape into red tape (stuff it into a bottle of red ink, and then hang it out to dry).

We had our share of glory, although now the name of the woman who shed it on us has been forgotten. It was she who submitted the winning design for the SHAEF shoulder patch (we became the Supreme Headquarters Allied Expeditionary Force when Gen. Dwight D. Eisenhower became commander). The flaming sword (the liberation armies) on a black ground (occupied Europe) surmounted by a rainbow of hope is still familiar, though the symbolism is largely forgotten.

We fell into some disgrace, too. We lost one woman private. The security officer gathered all of us women together one day and solemnly told us that one woman had been heard gossiping about our work, and ''So,'' he announced lugubriously, ''we have had to say goodbye to one of our number.''

Incidentally, the officers had to wave goodbye to one of theirs, too. He was guilty of writing (and, worse, losing) a parody of ''Overlord'' called ''Overboard'' that would have been good enough to tip a secret agent off to the real facts of the case.

Typing reports from secret agents in Europe may sound glamorous, but it quickly became rather boring. Information on the state of roads leading from the French beaches has a limited interest for the non-expert, however heroic the efforts to obtain it. Much more exciting was my guardianship of a list showing what facts could reveal the date or place of D-Day and the ways the Allies planned to thwart that possibility.

The cancellation of all leave could tip off the date, so that was why leave was constantly being canceled and uncanceled, to the chagrin of loved ones and the mystification (we hoped) of the German High Command.

As for place, the Nazis would naturally expect the landing at some spot where there was a suitable harbor, so the Allies built their own artificial versions (''Mulberrys'') and, to hide them from reconnaissance planes, sank them temporarily in the English Channel.

My father told me that we couldn't invade because there was no way to transport all the needed gasoline. I knew - and, oh, the delight of knowing more than he did - about PLUTO (Pipeline Under the Ocean), which would take care of that.

By the time D-Day rolled around, lifting the burden of that awful secret off us, SHAEF HQ had been moved. The women's barracks (we were rather proud of an old bomb that had buried its head in the floor) were about a mile's country walk through Bushey Park to where our offices were disguised under a camouflage net. A group of us walked through the park that June morning under a sky filled with aircraft. The fiery liberating sword had been unsheathed. And, since nature has its own sense of drama, the planes' roar was answered by hundreds of larks singing as they spiraled up from the meadow.