To the Editor:

Around 500 B.C., the Cretan seer Epimenides supposedly said, ''All Cretans are liars.'' Since Epimenides was himself a Cretan, this has been cited since as an ideal paradox, or circular self-contradiction.

In his letter of Dec. 25, Anthony Hecht objects that Bruce Duffy, writing on Wittgenstein, ruined the paradox by putting ''other'' before ''Cretans.'' But actually, Epimenides' statement is not a satisfactory paradox as it is usually phrased.

When in ordinary speech we call someone a liar or even a habitual liar, we mean that he lies when it pleases him or serves his purposes. For his every statement to be a lie is impractical. If all Cretans lied, say, 70 percent of the time, Epimenides' statement could fall within the 30 percent of truthfulness and raise no philosophical problems. To make the assertion paradoxical, Epimenides would have to say that all Cretans always lie, an assertion so manifestly absurd where any conceivable social reality is concerned that even a philosopher could not entertain it. In this latter case all we are left with is the knowledge that at least one Cretan lied once, and with that lie made a reputation that lasted 2,500 years. ROBERT GORHAM DAVIS Cambridge, Mass.