Wilders, a political veteran whose outspoken views have kept him out of power and under 24-hour security protection for years, won a clear mandate to lead government formation talks, taking 23% of the vote in Nov. 22 elections.

But if he is to become prime minister, he will have to convince potential coalition partners he is willing to compromise on long-standing calls to withdraw military support for Ukraine, slash spending on climate goals and scrap constitutionally-protected religious freedoms.

He needs backing from at least two more moderate parties to reach the required majority of 76 seats in the 150-seat parliament to form a right-wing government.

Much will depend on the willingness of outgoing Prime Minister Mark Rutte's conservative People's Party for Freedom and Democracy (VVD) and the centrist upstart New Social Contract of Pieter Omtzigt, both largely pro-European, to work with him.

Wilders has shaped Dutch policy for years from the opposition benches, tapping concerns about immigration and tying them to broader issues such as the cost of living, housing and healthcare. Mainstream centrist parties have already adopted tougher positions on immigration to avoid losing votes to the right, but none matched Wilders' frequent calls for a total ban on immigration.

Both the Netherlands' image in Brussels, as well as some policy changes in dealings with its EU partners, would be likely accompany a Wilders-led government. However, Dutch membership of the EU is not considered to be at stake as it is non-negotiable for Wilders' potential coalition partners.

"The Netherlands is always seen as a transparent, open, innovative and prosperous country with a very open society and this is suddenly a different tune we're hearing - we're seeing a more withdrawn and introspective side," said Kees van Rij, a former diplomat and advisor on international affairs at the Hague Centre for Strategic Studies.

"The question is if this will really change or if in the end, as is often the case in the Netherlands, compromises and interim solutions will be found," he added.

FOREIGN POLICY

The Dutch are known for their pragmatic politics, open economy and centuries of foreign trade. Under Rutte, the longest serving prime minister in Dutch history, the Netherlands was seen as a stable, predictable EU partner during turbulent times.

Wilders' shock victory signals that the Netherlands too is not immune to Europe's political swing to the right that has seen the rise of populists in Poland, Italy, Hungary and Slovakia.

His remarks about Islam and the Prophet Mohammad resulted in death threats. Fatwas were made against him and he has been forced to live with round-the-clock protection.

"Regardless of what the next Dutch coalition looks like, his victory will shift the political discourse, in the Netherlands and Europe," Eurointelligence wrote in a note on Thursday.

Among his party's campaign vows was to move the Dutch embassy in Israel to Jerusalem and immediately close its diplomatic office in the "corrupt" Palestinian Authority.

With his calls for "Netherlands first" and closed borders, Rene Cuperus of the Netherlands' Clingendael Institute think-tank called it "the Trump moment of Dutch politics."

"You can call it an earthquake. Nobody expected this result...not even Wilders himself," he said.

A Wilders-led government could make EU policy-making more difficult in several areas.

If he becomes prime minister, Wilder could seek to block increased payments to the EU budget, to which the Netherlands is a net contributor, putting at risk new money the EU wants to earmark for Ukraine and managing migration.

Wilders would likely also join forces with Hungary in demanding a much tougher EU stance on irregular migration and, like Slovakia, oppose providing more military equipment or money to Ukraine. The Dutch provided Kyiv with more than 7 billion euros under Rutte's premiership, including for F-16 fighter jets.

Finally, he would likely oppose admitting Ukraine, Moldova and the Western Balkan countries to the 27-nation bloc.

Much will depend on which of the slogans Wilders campaigned on survive coalition talks.

Dilan Yesilgoz, Rutte's replacement as the head of the VVD party, said on the evening before the election that she would not serve in any cabinet with Wilders as PM, though she did not exclude her party's participation.

New Social Contract party leader Omtzigt said he could not compromise with Wilders on ideas that would violate the Dutch constitution - notably the very first words of the first article, which forbid discrimination.

In earlier years, Wilders said he would scrap that article, along with banning head scarves worn by Muslim women and closing mosques and Islamic schools, but he has since vowed to seek common ground with other political parties.

(Reporting by Anthony Deutsch and Toby Sterling. Additional reporting by Stephanie van den Berg and John Cotton in The Hague and Jan Strupczewski in Brussels; Editing by Toby Chopra)

By Anthony Deutsch and Toby Sterling