BELGRADE, Yugoslavia - In what may be an attempt to buy time for Slobodan Milosevic, Yugoslavia's highest court invalidated parts of the presidential election on Wednesday after thousands of opposition supporters forced police to back off from seizing a strikebound mine.
The constitutional court ruling, reported by the state news agency Tanjug, came in a case brought by the opposition - which sought to have Vojislav Kostunica declared the winner of last month's election.
Instead, the court annuled ''parts'' of the election, the agency said, adding details of the ruling would be made public Thursday. If the presidential vote - or even parts of it - must be repeated, it means Milosevic retains power longer.
The announcement came on the eve of a planned mass rally in Belgrade that the opposition hoped would be the final push to force Milosevic to concede defeat.
Milosevic acknowledges Kostunica finished first in a five-candidate field on Sept. 24 but without a majority needed to avoid a runoff Sunday. The opposition has rejected a runoff.
Opposition official Goran Svilanovic said he believes the opposition will also not agree to take part in a rerun of the first round.
''We have our elected president,'' he said. ''These are things we can discuss, but my initial reaction is that there can be no bargaining.''
The opposition, challenging the official findings of the Federal Electoral Commission, went to Yugoslavia's highest court earlier Wednesday, appealing to the justices to grant them victory in the presidential elections.
The court met in emergency session Wednesday to hear complaints by the 18-party opposition coalition, maintaining Milosevic's supporters manipulated election results by using a sophisticated software program.
Opposition leaders said they had obtained a copy of the program and would use it to illustrate how the vote was rigged to favor Milosevic's candidacy.
Earlier Wednesday, Milosevic's police abandoned barricades at a striking coal mine 25 miles south of Belgrade and mingled with thousands of workers seeking to topple the Yugoslav president.
The turnout gave opposition forces hope that the regime was mortally wounded.
''The battle for Serbia was won here,'' cried one jubilant opposition leader, Dragan Kovacevic.
The stunning and swift turn of events at the Kolubara mine complex was unprecedented in a former communist nation with no history of major worker uprisings. It caught even top opposition figures off guard. They rushed to join more than 10,000 protesters at the mine and predicted Milosevic's quick demise.
Opposition leaders issued an ''ultimatum'' for Milosevic to resign by 3 p.m. Thursday - the time set for the Belgrade rally.
''This flame will engulf the whole of Belgrade,'' said Vladan Batic, an opposition leader.
In an open letter Wednesday to Milosevic before the court's ruling, Kostunica said ''it will be better for you to recognize'' electoral defeat or risk ''the danger of open clashes'' nationwide.
''Serbia has risen so that one man would leave,'' Kostunica told cheering workers and their supporters at the Kolubara mine.
Only hours earlier, police in riot gear had poured in and occupied the strip mine complex in an attempt to break up the largest of the nationwide strikes against Milosevic. But the police couldn't contain a swelling crowd that heeded the workers' cry for help.
With sunset approaching, the police gave up. Most withdrew from their barricades and were mingling with strikers inside the compound.
Supporters of the strikers streamed in on foot and in convoys of vehicles. One bus pushed aside a police car blocking its way.
A few police remained guarding some areas of the mine, but made no attempt to control the joyous crowd.
From the beginning of the civil disobedience campaign launched this week to force Milosevic to concede defeat in the election, the mine was a pivotal point. It employs 7,000 workers and supplies major power plants.
On Tuesday, the Milosevic government had threatened ''special measures'' against leaders of strikes and road blockades, and Belgrade's prosecutor issued arrest orders for 13 opposition leaders involved in organizing the walkout at the Kolubara mine. None of the arrests has been carried out.
The mine walkout was the forerunner of other strikes: the state telecommunications company workers announced they would stay off the job and city bus drivers and garbage collectors in Belgrade refused to work.
''This is (Milosevic's) end,'' said a Kolubara mine worker, Dragan Stamenkovic. ''Now the workers have risen.''
Before the court's ruling, the government was pushing ahead with plans for the runoff, where voters will mark paper ballots bearing the names of Milosevic and Kostunica. The opposition insists it is pointless to participate because Milosevic will simply cheat again.
In July, the Milosevic-controlled parliament changed the constitution, removing any requirement for a minimum voter turnout.
Prime Minister Momir Bulatovic, meanwhile, repeated the position that regardless of the election outcome, Milosevic can remain in office until his current term expires in June.
There were also signs that Milosevic's control over the media, until now the principal propaganda pillar of his regime, was fraying.
The main state-run daily in the northern province of Vojvodina declared Wednesday that its editorial policy would switch from following the government line to reporting on events objectively. Its Wednesday edition for the first time carried numerous reports on opposition activities.
