Pim Fortuyn, a maverick Dutch party leader whose anti-immigrant message won him a formidable political following, was shot dead tonight as he walked to his car outside Amsterdam.

Police arrested a man they said committed the crime, the first murder of a political leader in recent Dutch history. They released few details about the suspect, other than to say he was white, a native Dutchman and refusing to cooperate.

Fortuyn died 15 days after Europe's new racial politics delivered another shock, the second-place showing in French presidential balloting of far-right leader Jean-Marie Le Pen. President Jacques Chirac defeated Le Pen in a runoff on Sunday, but not before racial issues took top billing on the French political stage.

Fortuyn, 54, rose to prominence on a wave of apprehension that many Europeans feel as immigrants, most of them Muslims from Africa and the Middle East, put down roots in societies that historically have been largely white and Christian. Anti-immigrant parties have recently gained ground in Denmark, Germany and Italy as well.

Campaigning for the Netherlands' scheduled May 15 parliamentary election was suspended tonight, and the Reuters news agency said the Dutch cabinet planned to meet Tuesday to consider whether to postpone the vote.

"In God's name, let's keep our calm," an emotional Prime Minister Wim Kok told his country in a televised address, expressing shock that such a thing could happen in "our peace-loving Netherlands."

Small numbers of Fortuyn supporters clashed with riot police outside the parliament building. Police reported scattered incidents in which young people of North African origin were celebrating the killing.

Fortuyn had recently formed a political party, List Pim Fortuyn. Some analysts predicted that it might win one-sixth of the seats in the coming election -- a good showing in a multi-party system -- and that Fortuyn might become a behind-the-scenes kingmaker in assembling a new government, or even prime minister.

Fortuyn became a leading figure in little more than a year by challenging a Dutch tradition of tolerance that by and large has welcomed immigrants. He gave voice to widespread fears that the country of 16 million was being overrun by the newcomers.

Ethnic minorities now make up more than 10 percent of the total population, and more than a third in the largest cities, Amsterdam and Rotterdam. Most of the immigrants are from North Africa and Turkey.

Fortuyn opposed multiculturalism, saying immigrants must learn the Dutch language and integrate into Dutch society. He called for a halt to new arrivals until those already in the country had been fully assimilated.

In an interview with Reuters TV last week, he said that "everywhere in Europe, socialists and the extreme left have forbidden the discussion of the problems of the multicultural society. To identify the problem is to solve it."

Fortuyn, dapper and with a shaven head, was openly gay and in his campaign advocated tolerance of different sexual orientations.

He once called Islam a "backwards" culture because of its treatment of gays and women. That quote got him kicked out of his original party, Livable Netherlands. Then he started his own Livable Rotterdam party, which stunned political analysts by winning a third of the vote in local Rotterdam elections in March, taking 17 of 45 city council seats.

Born in 1948, Fortuyn studied sociology in the 1970s in Amsterdam, which had a thriving anti-capitalist counterculture. He became a college professor and called himself a Marxist. Later he shed that label and made a name as a columnist. In his campaign, he advocated continuing the government's broad role in managing the economy.

"He was a funny mixture," said a Dutch diplomat who knew Fortuyn. "He was a child of the '60s, a libertarian. He was open about his homosexuality. . . . He mobilized the angry white man of 45 or 50 years old. . . . What made him a right-winger was his criticism of Islam and immigration."

The diplomat said Fortuyn's message found a wider audience after last year's terrorist attacks in the United States and the arrest in the Netherlands of Muslims suspected of planning attacks in Europe.

Fortuyn told journalists several times in recent weeks that he had received written and telephoned death threats, which his spokesman confirmed tonight. In a televised debate a few days ago, he said he would not campaign in "no-go areas," crowded neighborhoods in Rotterdam where most residents are immigrants. He said the residents might beat him up.

Fortuyn reportedly called a friend today and told him he had received a threatening phone call and wondered whether to go home for the night or stay in a hotel.

Witnesses said Fortuyn was shot six times as he left a radio station in the town of Hilversum, a few miles southeast of Amsterdam, where he had just been interviewed. The gunman fled; paramedics treated Fortuyn at the scene but could not revive him.

In his home city, Rotterdam, supporters gathered at the city council chambers tonight to pay tribute. About 400 others went to Fortuyn's house in an impromptu show of mourning.

The deputy of Fortuyn's party, Joao Varela, could not hold back tears during a television interview. "He was like a father to me," he said. "He was very inspiring and could have made a difference for Holland."

Hans Dijkstal, leader of the People's Party for Freedom and Democracy, which lost many of its supporters to Fortuyn's new organization, said, "This is the absolute rock bottom for Dutch society and Dutch democracy."

Special correspondent Juliette Vasterman in Amsterdam contributed to this report.

Mourners leave flowers at Pim Fortuyn's Rotterdam home. His supporters clashed with police as the prime minister appealed for calm.Fortuyn was running in May 15 election.