(Updates with ceremony over, adds details, previous GRACANICA)

By Matt Robinson

GAZIMESTAN, Serbia, June 28 (Reuters) - Hundreds of Serbs in Kosovo marked an epic medieval battle central to their claim to the province on Thursday, avoiding feared clashes with ethnic Albanians angry at delays to their demand for independence.

NATO troops secured the route as U.N. police escorted several busloads of hardliners from the Serb stronghold of Mitrovica to religious services near the capital, Pristina.

But in a show of strength and a nod to the territory's de facto independence, the bulk of the extensive security operation was handed to Kosovo Albanian police.

Special units armed with Heckler & Koch assault rifles lined the road to the towering Gazimestan monument marking the site of the 1389 Battle of Kosovo, a defeat loaded with historic and religious significance for Serbs.

Police searched buses and confiscated nationalist T-shirts. At least one Serb was slammed on to a car bonnet and handcuffed.

The West sees no prospect of returning Kosovo to Serb rule after the ethnic cleansing and atrocities of the late 1990s. Albanian leaders have threatened to declare independence unilaterally if a diplomatic stalemate between the West and Russia at the United Nations drags on much longer.

"Those who wish to cut the heart from this people want to wipe them from this Earth," said Orthodox Bishop Amfilohije.

June 28, St Vitus' Day in the Serbian Orthodox calendar, is the date when Tsar Lazar's Orthodox Christian Serbs lost a battle to Muslim Ottoman Turks on fields north of Pristina.

HOLY WARRIORS

The defeat ushered in 500 years of Ottoman rule and became central to a Serb belief in their close links to God.

Late Serb leader Slobodan Milosevic exploited the battle six centuries later, riding the tiger of Serb nationalism into the wars that tore apart Yugoslavia and drew NATO bombs in 1999 to halt the killing of Kosovan Albanians.

Almost a million Albanians were temporarily driven out in a two-year Serb counter-insurgency war. Independent estimates put the civilian death toll at between 7,500 and 12,000, mostly Albanians. NATO forced Serb forces to withdraw and Kosovo has been run by the United Nations since.

Eight years later, Serbian ally Russia has blocked the adoption of a U.N. resolution that would set Kosovo on the path to statehood, raising fears among NATO powers of Albanian unrest.

Despite warnings from NATO and a ban by Kosovo's U.N. governor, a handful of Serbs wore T-shirts of the 'Tsar Lazar Guard', calling for "war for the liberation of Serbian land". Albanian hardliners had said they would be "met with bullets".

Around 100,000 Serbs remain in Kosovo, outnumbered by 2 million Albanians, mostly Muslim but overwhelmingly secular.

It was at the Gazimestan monument in 1989 that Milosevic addressed hundreds of thousands of Serbs in a speech that foreshadowed the bloody collapse of Yugoslavia in the 1990s.

One Serb group said it was honouring "the holy Kosovo warriors who fell defending Christian civilisation and the whole of Europe from Islam".

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