The Marxist-ruled republic of Serbia mobilized its police Saturday and said it would no longer recognize decisions by Yugoslavia's collective presidency, charging it was bent on the dissolution of the multiethnic nation.

Serbian President Slobodan Milosevic made the surprise announcement as two more members of the country's eight-man presidency announced their resignations and witnesses said battle tanks were brought into Belgrade.Three members have quit the presidential body since Friday to protest a decision by its majority to reject a military request for emergency power to intervene in a dispute between Yugoslavia's six republics.

Yugoslav President Borisav Jovic, Serbia's member of the body and chairman of the joint presidency, resigned Friday. He was followed Saturday by Nenad Bucin, Montenegro's representative, and the representative of Serbia's Vojvodina Province, Jugoslav Kostic.

The five remaining members of the presidency convened late Saturday - over the objections of Jovic, who said his resignation was not yet official - and agreed to meet "as soon as possible" with the leaders of the republics to discuss the crisis.

Nationalist-minded republics such as Slovenia and Croatia are advocating the breakup of the Yugoslav federation, while communist-ruled Serbia leads those demanding the preservation of the union.

The independence-minded republic of Slovenia charged the resignations were part of a Serbian plot to sabotage the political system and justify an army takeover to preserve the union in which the 8.5 million Christian Orthodox Serbs are the dominant ethnic group.

Slovenia and Croatia placed their police forces on top alert, with paramilitary officers taking positions around key buildings.