WHEN SOMEONE vanishes in Washington, we know what to do.We round up the usual suspects.

The mugging possibility leaps to mind. But the police blotter shows nobody by the name of April with flowers in her hair and credit cards strewn all over the sidewalk.

Qaddafi? He's always good, for a rumble. He may have sent a hit squad over to sabotage spring. It would be like him.

Did James Watt ban her? The secretary of the interior takes seriously his responsibilities to keep the Mall free of the "wrong element," and it is true that when April does her usual number here, there's a great deal of kissing in the streets, loitering, aimless smiling in the parks, unfocused and unsettling civility.

We also check all the congressional committees to see if spring somehow got bottled up in one of them. Say there was a resolution pending in favor of the coming of spring. Somebody would be bound to object -- it is difficult to distinguish oneself, particularly in the House. Someone would insist on "an open rule," which would mean it could be amended into the ground, like the nuclear freeze.

The Senate floor is another Death Valley. You saw what happened to the proposal to withhold taxes on interest and dividends, which was something that even Ronald Reagan and Teddy Kennedy agreed about. The bankers roared, and the Senate caved.

Maybe the moneybags don't like spring, either. People often think about getting married in the spring. Next thing you know, they want to build a house. That means they'll ask for a loan. Maybe the bankers did a mail campaign against the vernal equinox. Senators, as Bob Dole said, are not made of steel.

The maddening thing is that everyone knows April was here. You can look anywhere and see her traces: daffodils, tulips, the lacy buds on the trees. But her heart was not in her work. She forgot the dulcet zephyrs. She forgot to turn up the thermostat. She borrowed leaden, lowering skies from November. She did not laugh her girlish laughter, and there was nothing girlish about her tears. She dumped icy buckets on us. This girl was not Botticelli's Primavera. More like Medea she was, full of raging tempests.

For gardeners, it was the cruelest month, passed hunched by the window watching the rain. Who can dig in the dirt wearing mittens. The sound track was silent. No arias from the mockingbirds. They got their overcoats back from the cleaner like the rest of us, and huddled in their nests.

There is a theory, of course, that April is a liberal, who looked up from her exterior decorating long enough to see what was going on -- and hurled herself on the first bus she saw heading out. It happened to be carrying a high school band from Tuscaloosa, and she passed herself off as a flautist.

Some thought it was the flowering of the secret war in Nicaragua that caused her flight; others, the prospect of the MX about to bloom again.

Whatever it was, she flounced off, leaving us with the bitter reminders of what ought to be. Everyone else did their part, according to the rites. The tourists came, their children bundled in parkas and scarves. They gamely trudged through the halls staring at statues of people they thought they ought to know, trooping in and out of the galleries to watch and empty, idled Senate, grateful to be out of the gales that swept the Capitol plaza.

The cherry blossoms came out, exactly as they should, although the rough winds shook the darling buds something Shakespearean. It rained on our parade, our princesses smiled through their rattling teeth.

No interdepartmental task force was appointed to investigate what ailed April. Maybe she was being audited by the IRS. Possibly she heard one too many Democratic candidate promise "a reform of the infra-structure."

Now that she is about gone, she should start thinking about next year, get herself a new agent or a different PR firm. People come here and are disappointed for all sorts of reasons, but they don't just quit.

She could have had a press conference at the National Press Club, even laid on coffee and Danish to prove her seriousness. She could have sheedled a "Dear Colleague" letter out of a congressman; somebody up there has got to be unequivocally in favor of spring. She could have written an op-ed piece, or at least a letter to the editor. She could have gone on a talk show with Joel A. Spivak, or even Phil Donahue, who could have earnestly canvassed the good things and the bad things about April.

May's up next. Let's hope she has her wits about her.