BRUSSELS -- European Union leaders met here Tuesday night under intense pressure to overhaul the way the bloc is run, after populist upstart parties on the right and left surged in four days of legislative elections ending Sunday.
Looming over a dinner attended by the leaders was the drubbing handed to mainstream parties in the European Parliament voting by groups such as the National Front in France and the United Kingdom Independence Party, which are seeking to diminish, or even dismantle, the six-decade effort to integrate the Continent. The main issues at the dinner -- the leaders' first meeting after the balloting -- were expected to be how to craft future EU policies in the face of such anti-European election results, and how soon to choose a new European Commission president to replace the departing Jose Manuel Barroso.
Selecting the next head of the commission, the bloc's main policymaking arm, marks "a critical moment for the EU in terms of signaling how leaders are responding to the rise in populist anti-EU sentiment," said Simon Hix, London School of Economics professor.
But the dinner could mark the start of another potential crisis for the union over the issue of who gets the right to choose the candidates who run its day-to-day affairs, including the president.
For the first time, the European Parliament's leading parties have formally put forward their own candidates for that job. One of those is Jean-Claude Juncker of the center-right European People's Party, which won 213 seats. Mr. Juncker is expected in the coming days to try to form a majority. The runner-up group in the polls was the center-left Socialists and Democrats group, with 190 seats.
"If you want to respect the new democratic way of choosing commission presidents, you'd pick Juncker, but Juncker looks very much business-as-usual when it comes to responding to growing public opposition to Europe," Mr. Hix said. "So it's a very tricky dilemma."
The commission presidency is a powerful role, and the Parliament's bid to decide the post marks a sharp break with the past, when it was assumed that government leaders would assign the top EU jobs behind closed doors.
The president, who will eventually need the Parliament's approval, gets to set the tone at the top of a body that proposes legislation in a huge number of areas, including EU migrants' rights, social security and bankers' bonuses, and gets to represent the bloc jointly with the president of the European Council, the group representing EU leaders, at important international gatherings.
Importantly for national governments, the president also plays a key role in allocating portfolios such as trade, competition, financial services, monetary affairs and digital policy at the top of the commission's hierarchy.
But there are deep misgivings, particularly in Britain, about whether Mr. Juncker -- a former Luxembourg prime minister who has strong federalist leanings -- could deliver the kind of changes to the EU that would enable Prime Minister David Cameron to persuade voters to keep Britain in the bloc in a promised national referendum on the issue in 2017.
Yet another factor weakening the Parliament's claim to name the commission president is that both Mr. Juncker's party and the Socialist group, which has put forward the current Parliament president, Martin Schulz, as its candidate for the commission, lost seats in the election.
Even so, other leaders, including Spanish Prime Minister Mariano Rajoy and Austrian Chancellor Werner Faymann, expressed some support Tuesday for Mr. Juncker.
As in the past, the leaders will probably agree on the nominee by consensus, but that could take time.
Among the center-right alternatives to Mr. Juncker discussed in recent weeks are Jyrki Katainen, the Finnish prime minister; Enda Kenny, the prime minister of Ireland; and Donald Tusk, the Polish prime minister.
Some diplomats have also suggested that nominating a woman to the post might break a looming deadlock with the Parliament. That has generated speculation about the prospects for Christine Lagarde, the International Monetary Fund managing director; newly re-elected Lithuania President Dalia Grybauskaite, and Danish Prime Minister Helle Thorning-Schmidt.