Is there no one old enough on The Post's copy desk to have drunk a martini? Is your Health section written and edited entirely by the pot-smoking generation?

What other explanation could there be for both text and table of an article on alcoholism by Wendy Melillo defining a martini as consisting of ''one part gin, one part vermouth''?

President Franklin Roosevelt, who was described as having served a wartime martini to Stalin, was notorious for the weakness of his concoctions. But surely he never stooped to a half-and-half formula.

To add vile insult to sloppy research, the equal-parts definition comes immediately after a quote from the sainted Bernard DeVoto. The writer could not possibly have read and been untouched by DeVoto's tribute to the martini in his Harper's magazine column and in a 1952-era book titled "The Hour." Some of my friends who sensibly gave up hard booze regularly reread DeVoto with reverence just to feel ennobled at the magnitude of their sacrifice.

''There is a point at which the marriage of gin and vermouth is consummated,'' DeVoto wrote. Taking a small liberty with his formula, for an 80 proof gin it would come to about 4.7 to 1.

''If you use less gin, it is a marriage in name only and the name is not martini. . . . Happily, the upper limit is not so fixed; you may make it a little more than that . . . which is a comfort if you cannot do fractions in your head and an assurance when you use an unfamiliar gin,'' DeVoto wrote.

''But not much more. This is the violet hour, when the affections glow and valor is reborn, when the shadows deepen along the edge of the forest and we believe that, if we watch carefully, at any moment we may see the unicorn. But it would not be a martini if we should see him.''

In the spirit of research, I would invite Melillo to join my wife and me at the Press Club bar when the sun has dropped below the yardarm. For a real martini. Possibly two, for a special occasion. But no more. Unicorns seen can be disillusioning. -- David L. Perlman