The European Union official overseeing Turkey's admission to the 25-nation bloc warned yesterday that Turkey's prosecution of a bestselling author for insulting "Turkishness" could damage the country's chances of joining the EU.

"It is not Orhan Pamuk who will stand trial, but Turkey," EU Enlargement Commissioner Olli Rehn said in an unusually blunt statement released in Brussels. "This is a litmus test of whether Turkey is seriously committed to freedom of expression and to reforms that enhance the rule of law."

Pamuk, 53, Turkey's best-known novelist, is expected to go on trial today for stating in a Swiss magazine interview what most historians regard as unassailable facts: That some 1 million Armenians were slaughtered by Turks in the 1915-1918 genocide and that thousands of ethnic Kurds have lost their lives in more recent civil strife in modern Turkey.

The case has stirred outrage across Europe, where there is deepening opposition to allowing Turkey whose population is largely Muslim and whose landmass lies almost entirely in Asia to join an economic and political confederation whose most basic membership requirement is a commitment to democracy and to such values as freedom of speech.