Yugoslav Communist leaders pleaded for calm and warned of a possible crackdown after rival Serbian and ethnic Albanian demonstrations Saturday drew hundreds of thousands of people.

In Belgrade Serbs mounted the biggest demonstration in Yugoslavia's history to protest Albanian nationalism in Serbia's autonomous province of Kosovo.Soon afterward almost 100,000 ethnic Albanians staged a counter-demonstration in the Kosovo capital of Pristina.

The Yugoslav news agency Tanjug said the situation in Pristina was growing more tense by the hour.

It said the crowd included "well-known irridentists" - Yugoslav parlance for ethnic Albanians who want to annex the province to neighboring Albania.

Police reinforcements were rushed in as the crowd swelled, and Pristina sources said riot police were on standby.

Federal and provincial authorities met to decide on whether to take "temporary measures."

Kosovo Politburo member Hasim Redzepi appealed to the crowd to go home, saying that if they did not "it could lead to a serious deterioration."

For the third day running the crowd demanded reinstatement of local leaders forced from office by Serbia last week to take the blame for the growth of Albanian nationalism and alleged persecution of Koso-vo's Serbian minority.

Serbs are pressing to get back control of Kosovo, which won sweeping autonomy from the republic under the 1974 constitution. They want constitutional reforms to reverse the situation.

Slobodan Milosevic, the populist Communist Party chief of Serbia, Yugoslavia's biggest republic, won cheers and applause when he told the Belgrade rally: "We will win the battle for Kosovo."

"We are not afraid of anything," he said. "The leaders will listen to the people, or time will sweep them away. The most important task today is to create peace and order in Kosovo."

He drew parallels with the Spanish Civil War period.

Organizers said 1.3 million people joined the rally but witnesses put the figure at about 600,000. Whatever the figure, Tanjug said it was Yugoslavia's biggest ever.

"People may accept poverty but not the loss of freedom," said Milose-vic. "It's no time for sorrow but for fighting."

The Serbian protest was railed against what was called the incompetence of Yugoslavia's ruling communist elite and their failure to unite to solve Yugoslavia's economic crisis.