Serbia's first pro-democracy president since World War II took office Sunday, vowing to bring stability to the Balkan republic and push it closer to the European Union (search) and NATO.

Boris Tadic (search), 46, leader of opposition Democratic Party, was elected in a June 27 runoff, defeating a hard-line nationalist ally of former President Slobodan Milosevic (search).

Although the office is mostly ceremonial, Tadic's election was seen as a signal of Serbs' desires to more closely align with the EU and NATO and to move away from the nationalist isolation of Milosevic's autocratic legacy.

Taking his oath of office in the Serbian parliament Sunday, Tadic said the republic's leaders "must know our national priorities: they are our intentions to join the European Union, to provide a better life for our people."

"The stability of this society is the best guarantee for its prosperity," Tadic said, promising to "be the president of all of Serbia's citizens."

After being sworn-in to applause and hand shakes from well-wishers, Tadic crossed the street to Serbia's presidential offices, striding past an honor guard.

Delegations from 40 nations attended the ceremony, including the foreign ministers of Austria, Greece and Slovakia, as well as defense ministers of Macedonia, Bulgaria and Romania.

Also there were Erhard Busek, the head of the Stability Pact for Southeastern Europe, Adm. Gregory Johnson, the region's NATO commander, top officials from Montenegro, Serbia's partner republic and religious and other dignitaries from both republics.

Tadic's victory was not the first time a Serbian president was chosen in elections, but it marked the first time since World War II that Serbs elected a pro-democracy candidate.

Milosevic had held the post in the 1990s before becoming the president of Yugoslavia, which was replaced last year by Serbia-Montenegro. After Milosevic, Serbia's presidency then went to Milan Milutinovic, one of his allies. Both men are now in The Hague, Netherlands, at the U.N. war crimes tribunal to answer charges stemming from the Balkan ethnic conflicts of the 1990s.

Soft-spoken and telegenic, Tadic is also seen as the man who will carry on the reformist legacy of the late Zoran Djindjic, Serbia's first post-communist prime minister. When Djindjic was gunned down in 2003 in Belgrade, many believed it spelled doom for Serbia's fledgling democracy.

Serbia faces tough times ahead as it struggles to counter a stagnant economy and a resurgence of nationalism tolerated by some top figures in Serbia's conservative government.

The government, headed by Prime Minister Vojislav Kostunica, relies on the support of Milosevic's Socialists in parliament. But Tadic's win was expected to counterbalance some of the influence wielded by the Socialists.

Kostunica, who considers the U.N. war crimes tribunal anti-Serb, is nonetheless expected to now work with Tadic who is pushing for Serbia to hand over suspects. Cooperation with the U.N. tribunal is the key condition for any U.S. and other Western political and financial support.

"There has been enough of misunderstandings with the world and discord in Serbia," Tadic said at the end of the ceremony, during which he kissed the Serbian flag. "We must make big strides forward to make up for lost time."

Tadic's term is five years.