DURING THE morning rush, one gray and chilly day last week, the sound of a flute came floating down into the McPherson Square Metro station. As Metro's customers were borne up the escalator toward the site of the daily struggle, the music met them more than half way. A young flautist at the top of the stairs was playing with spirit; his hat was on the pavement in front of him.

Perhaps it was a sign of spring. Last summer there were several lunchtime flutes and a variety of interesting percussion instruments around Farragut Square. A string trio occasionally appeared. There was a man with a guitar, who made people late for appointments by playing Vivaldi.

But should you encourage them by putting quarters in the hat? That is a matter of deep policy. The economy's in bad shape. The growth rate is low. Productivity is down. How are we going to get productivity up if people spend their time playing musical instruments in the street? Should those people not be sitting behind desks, writing numbers on pieces of paper, making phone calls and engaging in similar productive activities? Investment is doing poorly, too. If you invest a dollar in a hot dog, you've got something that you can carry away in your hand -- a tangible asset. But the same dollar's investment in flute music fades quickly -- except, of course, in the memory.

But, to argue the other side of the question, we acknowledge that a quarter contributed to street music increases the gross national product just as much as a quarter spent on beer, potato chips or any other necessity of life. Where, in the National Income Accounts, would that quarter be recorded? Clearly, it would be under Interest. Everyone has an interest in streets that are not only clean but civilized, and music makes any street corner more interesting. Conclusion: you have a positive civic duty to drop a quarter in the hat -- and two quarters when the music is Vavaldi.