MALMO, Sweden  Jimmie Akesson, 31, looks more like an up-and-coming advertising executive than a seasoned politician. But Mr. Akesson, the leader of the Sweden Democrats, does not believe in a soft sell: He wants to cut immigration by 90 percent, and he thinks that the growth of Sweden’s Muslim population is the country’s biggest foreign threat since World War II.

Sweden, which is seen by many people as a guardian of liberalism and tolerance, has never elected to Parliament a member of any party who campaigned openly against immigration. That could change in elections on Sunday.

Opinion polls suggest that the Sweden Democrats will exceed the 4 percent threshold needed to reach Parliament. An alliance of center-right parties appears to have a narrow overall lead, according to the surveys, but the Sweden Democrats could hold the balance of power, something that could create a political crisis.

That prospect has jolted a nation in which even some of Mr. Akesson’s fiercest critics now acknowledge that too little has been done to integrate immigrants. Political analysts also say that the rise of the populist right shows that Sweden is being buffeted by broad political currents familiar in other European countries.