FEBRUARY is a gray plain of a month, broken only by Valentine's Day, which, as we all learn in the second grade, can be super or the pits, depending, in childhood, on how many cards you get and, later in life, from whom.

A pre-Valentine tour of the card shops brings you in close touch with the trends in relations between the sexes. I am drawn to a tentative conclusion that once you get beyond the happy, stable, hearts-and-flowers couples, things have taken a turn for the assertive, the forthright and the explicit. Beating around the bush is out.

One other thing seems pretty clear, too. Unrequited love, the stuff of myriad medieval ballads, and occasional country-western laments, has been rooted out of our society.

There was a time when the lovelorn had recourse to a card that owned up to a regrettable imbalance in the affections of two people.

Outside, in big, red, threatening letters, "IF YOU WON'T BE MY VALENTINE . . . " Inside in tiny, abject type, "I'll still be yours."

A diligent, week-long search has turned up only one that even touches on this troublesome romantic theme.

I hate to tell you, but it is a valentine featuring Richard Nixon. I realize that the lovesick might, at the sight of the familiar lowering jowls, drawn in black-hatched grey by the incomparable Oliphant, have all tenderer thoughts driven from their minds. Still, it may have to do, because textually, it is the only thing I have seen that comes near expressing the plight of those suffering what Shakespeare called "the pangs of disprized love."

Under the drawing of our national bad penny is printed, "Just thought You'd like to know . . . " Inside, it says, "I'm still around."

Yes, I know, it is a little political for some tastes. It also has a jarring topicality, since our most shameless president is in the process of making yet another comeback which we must all share, this time as a commentator.

That sort of thing is, incidentally, what people have against February. Along with sudden, vicious, uncalled- for snowstorms, it brings tidings that Richard Nixon is going to be on your homescreen, telling you what other politicians are doing wrong.

But back to the racks. The replacement for yesterday's naked plea for affection is today's vindictive Valentine, which comes to us from Bittersweet Cards, Inc. It shows that rejection is not only survivable but can be turned into a good sharp kick in the ankles by a healthy ego.

Over the depiction of a woman obviously left in the lurch, the legend is, "I'm sorry you left me." At her feet is the kicker, "I wanted to leave you first."

The card shop tour is instructive in larger ways. The more you browse, the more you see that letter writing, doomed by the telephone, is getting the coup de grace from the anonymous scribes of the greeting card industry. Every year, they hone their art. A valentine for your great-granddaughter, a sick card for your brother-in-law who broke his leg, these are primitive staples.

But did you ever think you would see a valentine that also addresses your feelings about February? Well, it is here.

"Fight Feb. Blahs" is the headline. Below, a heart-bordered box sorts out valentine options.

"Either we can get together for some chocolate candy, or we can get together for some "you know what." Inside it leers, "Candy is bad for your teeth."

I want you to know that "you know what" is a euphemism of the most delicate, even Victorian, circumlocution in the context of the new X-rated valentine section, where the same invitation is couched in four- letter words.

Today's greeting card writers are determined that no one should ever take pen in hand again. Why put yourself through the agony of composition when everything you ever needed to say to another human being is already in cold print -- and available for 75 cents.

Is the relationship in the early stages? How about an item from the "Secret Thoughts" line? Alongside an embossed rose, here's a declaration of where you're coming from: "I hope I'm not being too forward, but I had to do something to let you know . . . I'm interested." Beats tremulously inscribing "Guess Who?" under a pierced heart, doesn't it?

The end of the affair? Come with me. See the loony bird shoveling earth over a buried bed.

The stark message inside: "It's over."

So useful for couples who have packed in a marriage or a meaningful relationship and wish to spare themselves endless explanation. They could send it out to their friends, and insure not being invited to the same parties any more.

Or, maybe one could send it as a valentine to the other. It's February, you know.