Vuk Draskovic, the leader of Serbia's largest opposition party, said today that he will not appear at a major rally scheduled here Thursday to demand the resignation of Yugoslav President Slobodan Milosevic.

Planning for the demonstration, seen as a test of opposition strength, has been plagued by disarray in the ranks of anti-Milosevic forces, as well as by intensified counterattacks by the government. Draskovic's refusal to participate was the latest sign of internal squabbling that has raised questions about whether anyone can provide an alternative to Milosevic and channel the popular discontent that has surfaced over the past few weeks across Serbia, Yugoslavia's dominant republic.

"August 19th will show whether Serbs prefer to lick ice cream or change the regime," said Darko Brocic, a pollster here.

Draskovic said he will send another leader of his Serbian Renewal Movement to the rally. The official explanation for this from the man whose fiery oratory earned him the title "czar of the streets" was that his replacement, Spasoje Krunic, is a better public speaker.

Other opposition figures said that Draskovic dropped out because a rival coalition of small opposition parties, the Alliance for Change, insisted on naming Velimir Ilic, mayor of the central Serbian city of Cacak, as one of its speakers. Ilic split with Draskovic a few years ago and formed his own party.

For his part, Ilic also did not seem enthusiastic about the rally. He said it was "organized too soon" and was likely to be "yet another wasting of the people's energy." At the same time, he likened Draskovic to "a spoiled baby" and said that "until someone deprives Draskovic of a microphone, there will be no democratic changes in Serbia."

The rally is being organized by the Group of 17, an association of independent economists. Their platform calls for Milosevic's resignation; for a transitional government run by people currently outside the political system; and for national elections within six months. Organizers said the demonstration will set a deadline for Milosevic's resignation and call for escalating protests if he refuses. In a formal notification to Belgrade police, they said they expect more than 100,000 people to attend.

Thus far, the struggle between Milosevic and the opposition has been mainly a war of words, with each side accusing the other of being "terrorists" and seeking to foment civil war. Milosevic supporters also have accused the opposition of acting as surrogates for NATO, which waged a 78-day bombing campaign against Yugoslavia this spring, and of organizing the demonstration in honor of President Clinton's birthday, which falls on Thursday.

Serbian Prime Minister Mirko Marjanovic called the Alliance for Change "a terrorist organization" after one of its leaders, Vesna Pesic, told a crowd that the "Romanian scenario" would be used to get rid of Milosevic if necessary--a reference to the execution of Romanian President Nicolae Ceausescu and his wife following the 1989 uprising there.