THE CROCUSES are up. For all those readers who had begun to fear that this February was going to last forever, this development is to be noted carefully. The CPI--the Crocus Progress Index-- shows that the shoots in the survey sample are up to a median height of 0.58 inches. Those crocuses are what the economists call a leading indicator.

Leading indicators make no promises, but they point the direction in which things are going. Just as President Reagan, at his press conference, wisely declined to predict the precise date when the recession would end, neither does the canny crocus commit itself to the date when the blossom will appear. But the green shoots are clearly visible, above the mulch frosted with sleet, under a gray sky.

February was put in the calendar for the highly moral purpose of reminding the population that life is not all fun and games. It is not all lazy weekends, and lying on the beach. Some of it has to be serious, dogged and gloomy. That's February. It's function is to make you feel, when you get a holiday, that you've really earned it. If it weren't for the sleet, who could really appreciate the sunshine?

Many of our readers seem to feel that this purpose has now been more than adequately fulfilled by the present winter. Many are calling for a change. Public opinion polls indicate a strong swell of sentiment in favor of no more ice on the roads, and something a bit more similar to last weekend's brief interlude. They will have to be patient. These things can't be hurried. February has, the last time we counted, 100 days or so, and six or eight weeks of it have already passed. It won't go on forever. How can you be sure of that? Keep your eye on those crocuses.