BELGRADE, Yugoslavia - Encouraged by cheering crowds, a convoy of 60 trucks blocked a key highway Sunday as opposition forces sought to gather support for a nationwide strike aimed at showing President Slobodan Milosevic he must relinquish power.
The trucks - taking part in a ''dress rehearsal'' for a series of full-scale blockades planned for Monday - were greeted by jubilant supporters as they passed through the opposition stronghold Cacak in central Yugoslavia. Some people tossed flowers as the trucks headed to an important highway linking Belgrade with southern Yugoslavia.
The truckers brandished banners and posters of Vojislav Kostunica, whom the opposition and Western leaders insist trounced Milosevic in Sept. 24 elections. Milosevic rejects the claims and says a run-off election is needed Oct. 8.
Smaller, traffic-snarling blockades were held at main intersections in the capital Belgrade. Drivers honked horns and pedestrians blew whistles and shook toy rattles - playing on a local expression for something broken beyond repair.
''No way are we going to settle for a run-off and that is now the law for everyone in this country,'' said Velimir Ilic, the mayor of Cacak, an industrial town of 80,000 people. Later Sunday, about 10,000 opposition supporters gathered at the main town square for a seventh consecutive night of anti-Milosevic rallies there.
''Our victory is as pure as a diamond,'' Ilic told the crowd. ''Kostunica is the elected president and we must persist in our resistance.'' He called for a total blockade of the town Monday.
Opposition leader Milan Protic urged people to come out into the streets Monday, stay away from their jobs and keep their children away from school. Protic acknowledged that it would take time to build momentum among a public drained by years of conflict and economic misery.
Protic, the opposition candidate for Belgrade mayor, said the protest leaders would try to escalate the tempo systematically ''until Milosevic realizes that he is no longer president.
In Washington, the National Security Council spokesman P.J. Crowley said the Milosevic opposition is ''getting stronger.''
''They are sending a strong message to Milosevic: 'Your time in office is over,''' he said.
But the cautious pace of the opposition's campaign raises questions about whether they will have the momentum to carry out their threats of bringing the entire country to a complete standstill.
Authorities in Yugoslavia's main republic, Serbia, warned students against joining the Monday strike, saying ''events disrupting school activities'' for political purposes ''are illegal.'' Students in Nis and other cities walked out of class during protests last week.
Workers have also walked out in vital sectors: the largest coal mine, a key oil refinery, railway lines. The strikes raised the prospect of power and fuel shortages. The independent Beta news agency said about 1,000 workers in another coal mine in Kostolac joined the strikes Sunday.
The government urged miners Sunday to return to work because a prolonged stoppage could effect electricity supplies since the country relies heavily on coal-fired power plants.
International pressure continued to build on Milosevic, who had rejected an offer of high-level mediation by close ally Russia.
The president of neighboring Romania, Emil Constantinescu, urged Milosevic to concede defeat and congratulated Kostunica for his ''historic victory.''
Opposition leaders, using figures from their poll watchers, claim Kostunica won the election with 51.34 percent to 36.22 percent for Milosevic. But the Federal Electoral Commission, in a tally criticized by the United States and other countries, says Kostunica fell short of the majority needed to avoid a runoff.
Even Russian President Vladimir Putin - one of Milosevic's last major allies - appeared to move toward the Western view that the Yugoslav leader was finished.
In Berlin, the German government said Putin and Chancellor Gerhard Schroeder spoke by telephone late Saturday and agreed that ''Kostunica's election victory emphatically expresses the will of the Serbian people for a democratic change in Yugoslavia.''
There was no comment from the Russians, and the foreign ministry Sunday repeated Moscow's position that Yugoslavs themselves should ''decide for themselves'' the outcome of the election.
Milosevic turned down an offer by Putin to send his foreign minister, Igor Ivanov, to Belgrade to meet with both sides. But two senior Russian diplomats - Vladimir Chizhov and Alexander Tolkach - arrived in Serbia late Saturday. The state Tanjug news agency reported Chizov visited Kosovo on Sunday and was to have official meetings in Belgrade the following day.
