TOCKHOLM, Sept. 14 — In a significant setback for a more unified Europe, Swedes voted overwhelmingly today to reject membership in the European single currency after a passionate referendum campaign, made uncertain to the last moment by the assassination of Foreign Minister Anna Lindh.

The margin of victory for those opposed to adoption of the single currency, the euro, far exceeded the expectations of many people here. It provided a stunning defeat for Prime Minister Goran Persson, who had called the referendum in the belief that most Swedes would agree to abandon their currency, the krona.

Political experts said the impact would be felt across Europe, countering efforts to strengthen the 15-nation European Union before its planned expansion with 10 new members next year. Apart from Sweden, two union members, Denmark and Britain, are outside the 12-country euro-zone stretching from the Arctic Circle to the Mediterranean.

European leaders interpreted the outcome as a signal that they had not swung Swedish opinion behind the broad project to transform Europe into a more cohesive and integrated force. "This was a result worse than I expected," Romano Prodi, the head of the European Commission, told Swedish television tonight. "It was about more than the euro. The euro is a symbol of more integration. This was a moment of prudence, not integration. We have to meditate how to explain better what we are doing."

With ballots tallied from all 5,976 voting districts, the anti-euro campaigners secured victory with 56.1 percent of the no votes to 41.8 percent for accepting the euro. The result suggested that Swedes had not been swayed by the killing of the fervently pro-euro Ms. Lindh and had avoided a sympathy vote in favor of the single currency.

Ms. Lindh died of stab wounds after an unidentified assailant attacked her as she shopped in a department store in central Stockholm on Wednesday.

Shortly before the final tally tonight, Mr. Persson appeared before reporters to acknowledge the defeat of the "yes" campaign.

"In this result we can see a deep skepticism toward the entire euro project among the Swedish people," he said. "It was a clear expression of the people's will."

Indeed, many experts had depicted the ballot today as a kind of judgment on eight years of Swedish membership in the European Union. So the outcome suggested a profound disenchantment with the idea of moving closer to other European nations. "There's a bigger fear for the new than we expected," said Ulrika Messing, a government minister.

Experts had always calculated that a "no" vote in Sweden would strengthen anti-euro sentiment in Denmark and Britain, delaying efforts in those two countries to hold referendums of their own, and therefore depriving the currency of broader economic and political backing.

Denmark rejected adoption of the euro in a referendum three years ago and its leaders had been monitoring the vote here for any indication of pro-euro enthusiasm that might encourage them to hold a fresh euro ballot in their own country. The margin of the vote seemed certain to disappoint them.

Britain has yet to decide when to hold a vote among its people and, with Prime Minister Tony Blair embroiled in political turmoil after the war in Iraq, experts in Britain have suggested that there is little likelihood of a major government initiative to swing a euroskeptic nation behind the euro. The Swedish government had said it would not hold another vote on joining the euro for 10 years.

The Swedish referendum came as the European Union has been working on a new constitution to underpin its expansion to 25 members. Across the Baltic Sea from Sweden, the tiny former Soviet republic of Estonia voted by a 2-to-1 margin in a separate referendum today in favor of being one of the 10 new members of the European Union next year.

The campaign leading up to the Swedish ballot had threatened to be overwhelmed by the death of Ms. Lindh, whose killing stunned Sweden, rekindling memories of the slaying in 1986 of Prime Minister Olof Palme. The police said today that they had not arrested a suspect in her killing.

Until her death, opinion surveys had shown the "no" campaign firmly ahead by 10 to 15 percentage points. That margin seemed to have survived intact despite a last-minute flurry of opinion surveys suggesting a "yes" vote was still possible.

The debate about the euro has been so fractious that five members of Mr. Persson's government spoke out against it, dividing the Social Democrats, who have led Sweden for most of the last 70 years. The vote, highlighting differences between young people, particularly women, who voted against the euro, and older Swedes, especially men, in favor of it, did little to heal the rift.

"Sweden is divided," Mr. Persson said tonight.

He had called for broad participation in the ballot to demonstrate Sweden's determination to resist violence and strengthen its democracy. The vote took place on a bright, late-summer day when the sunshine drew many people to sidewalk cafes in the capital and lakeside resorts across the land. More than five million of the seven million eligible voters cast their ballots, at least one million of them by postal vote before Ms. Lindh's death.

Almost like pilgrims, scores of people gathered outside the NK supermarket where she was killed. What began there as a few single roses laid by sympathizers last Thursday had grown by today to a four-foot-high, wreathlike shrine of flowers, candles and messages. Three days after she died, people still lined up to sign a condolence book.

"I was very sad when I heard about this and thought we must do something to show our support," said Ulrica Sjobladh, 36, a nurse who said she voted in favor of adopting the euro before signing the condolence book. She favored the euro, she said, because "we must all have the same opportunities, and the Swedish politicians can't decide for us.

"We should be inside Europe," she added.

Hanna Lindgren, a 26-year-old office worker in a pharmaceutical company, said that since Sweden had already joined the European Union in an earlier referendum in 1994, "we should be in Europe all the way.

"I'm a little bit worried that we'll lose a little independence, but it'll be good for jobs and for our welfare state," she added.

Before the vote, the "yes" campaign had been sponsored by the political and business establishment and backed by most newspapers and intellectuals, who had argued that euro membership would boost trade and employment.

But the insurgent "no" campaigners insisted that Sweden would not benefit as a euro member from being forced to adopt eurozone interest rates, 0.75 percentage points lower than the current Swedish rates, and needed economic independence to maintain its modest growth at a time when the major continental economies are in the doldrums.

"It is better for us to stand aside," said Bo-Goran Karlsson, a 57-year-old social worker who said he voted against adopting the euro. "We can trade with Europe but we don't want to be too close."

Many experts had described the ballot as, effectively, a display of how Swedes felt about the European Union itself some nine years after voting 52.6-46.8 percent to join it.

"There's no symbiosis between us and Europe," Mr. Karlsson said.