BELGRADE, SERBIA - A few weeks ago, members of a liberal resistance group here scattered ashes over their heads, an act of penance, they said, for electing Vojislav Kostunica, the prime minister who helped overthrow Slobodan Milosevic but who has since adopted Milosevic's harsh nationalist language.

The symbolism was clear: Kostunica, a brooding constitutional lawyer who wants Serbia to reject the West and turn east toward Russia, had forsaken the liberal aims of the October 2000 revolution. Now, they warned, as he runs for re-election, he is threatening to turn Serbia back into an economic and political pariah, a lonely nation at odds with much of the world.

Serbs will vote today in parliamentary elections that have become a tug of war between old-guard nationalism and a European future, between East and West.

"This is the most seminal election since the revolution when Milosevic was overthrown," said Foreign Minister Vuk Jeremic, a member of the pro-Western Democratic Party of President Boris Tadic. "For the first time, voters face a clear-cut choice between choosing Europe or choosing isolation."

Kostunica's nationalism, like that of millions of Serbs, has been heightened by deep and genuine anger over Kosovo's declaration of independence from Serbia in February, with the backing of the European Union and the United States. Serbs regard Kosovo as their medieval heartland. Many in Serbia consider its declaration of independence a reckless breach of international law.

At a rally of several thousand people Thursday night, Kostunica warned that allowing a Serbia shorn of Kosovo to turn toward Europe and the West would be treasonous.

All major political parties are emphatic that Kosovo should remain part of Serbia.

While Tadic has used the Kosovo issue to press for closer relations with Europe and Washington, Kostunica and other nationalist party leaders say Serbia should turn to Moscow and China.