BUDAPEST (Reuters) - Hungary defied demands to apologize on Wednesday for vitriolic criticism of EU leaders, but a senior government aide suggested it was seeking compromise to avoid its ruling party’s ejection from the main conservative group in the European Parliament.

Manfred Weber, a German conservative who leads the European People’s Party (EPP) group, has threatened to expel Hungarian Prime Minister Viktor Orban’s nationalist Fidesz Party unless it apologizes for its anti-EU and anti-immigrant rhetoric.

The EPP is the biggest group in the European Parliament, and Weber is its candidate to succeed Jean-Claude Juncker as European Commission president if it remains the biggest after European elections in May. Weber has cast the issue of Orban’s rhetoric as a question of fundamental values ahead of the vote.

Hungary’s government has made hostility to immigration the main plank of its campaign, with billboards accusing Juncker and Hungarian-born U.S. billionaire George Soros of plotting to destroy European civilization by bringing in masses of Muslims.

Government spokesman Zoltan Kovacs suggested in a Twitter post that Orban was not prepared to back down despite Weber’s ultimatum.

“We listen to other opinions, includ(ing) Weber’s,” Kovacs said. “But more important than party discipline are the defense of European Christian values and stopping migration. On this, we cannot yield.”

But the premier’s chief of staff, Gergely Gulyas, hinted at a possible compromise, telling Reuters there were open lines to Weber and other EPP leaders to find a way to keep Fidesz in.

FILE PHOTO: Manfred Weber, member of the European People's Party, in Berlin, Germany, January 14, 2019. REUTERS/Axel Schmidt -/File Photo

“We hope that a strong and united EPP can embark on the next elections, including Fidesz, which has been its strongest member based on the past three elections,” said Gulyas, the most senior Hungarian politician to address the issue publicly to date.

“There are open and operating channels both with Manfred Weber and the most important leaders of the EPP. The parties that initiated and supported Fidesz’ expulsion... in our opinion we need a solution that satisfies them too.”

While Orban cultivates his image at home as a maverick who defies Brussels, Hungary also benefits from its influence inside the EPP. A possible compromise could see Fidesz tone down its posters and express some regret for rhetorical excesses.

Weber has also demanded that Hungary allow a university founded by Soros to reopen there after being forced to leave the country last year, although Fidesz has shown no sign of backing down over that.

“Our rules and laws apply to every institution of education in Hungary equally, no exceptions not even for the Soros university,” Kovacs said.

NOT ENCOURAGING

Weber told Reuters on the sidelines of a conference in Germany that the signals from Fidesz and Orban were “not encouraging”, and that honoring the EPP’s values would be more important than political tactics.

“We have made several attempts at bridge building, but Hungary has not taken any steps or effort toward us,” he said.

Tamas Deutsch, a Fidesz founder and long-serving member of the European parliament, told the private television channel ATV late on Tuesday Fidesz did not want to leave the EPP: “One crosses the bridge when one gets there. We have our political family. It is the EPP.”

Orban has long been at odds with Brussels over his hard-line stance on immigration and accusations - which he denies - that he is undermining the rule of law by asserting control over the courts, media and other institutions.

The EPP has 217 lawmakers in the 750-strong EU legislature, 12 of them from Fidesz. It is expected to remain the biggest parliamentary group in the May elections, although likely weakened, opinion polls show.

Far-right, populist parties are expected to perform well.