* Orban deflects EU criticism of Hungary
* Says critics lack evidence of wrongdoing
* Brussels sees attack on democratic principles (Adds quotes from Merkel, Barroso, Reding)
By Justyna Pawlak and Luke Baker
BRUSSELS, March 14 (Reuters) - A defiant Hungarian Prime Minister Viktor Orban dismissed criticism that changes his government has made to the constitution are anti-democratic, saying there was no evidence of any breach of European Union rules.
The EU, the United States and human rights organisations have accused Orban of using constitutional amendments to limit the powers of Hungary's top court and undermine democracy in the former Soviet satellite. The move follows steps last year to change Hungary's media laws and the retirement ages of judges.
Speaking before attending an EU summit in Brussels, Orban said Budapest was ready to explain the latest moves and challenged critics to produce concrete evidence of wrongdoing.
"Who is able to present even one single point of evidence -facts, may I say - which could be the basis for any argument that what we are doing is against democracy?" the conservative prime minister told reporters.
"Saying 'we don't like something' is not concrete enough to react... I am more than happy to answer their questions."
He faced more disapproval on Thursday, the first day of the two-day summit, where the main focus was economic policy for the 27-member bloc to tackle its sovereign debt crisis.
Many of his EU peers see the changes, which passed through parliament on Monday, as the latest effort by the nationalist leader to assert power over other branches of the state.
Since returning to office in 2010, Orban has defied the EU on principles such as media freedom and central bank independence, resisted pressure from the International Monetary Fund to change economic policies, and angered foreign investors.
European Commission President Jose Manuel Barroso reiterated his concerns to Orban during the meeting and said the EU executive would assess of the new rules to prepare its response.
"We will use all instruments in our competence to address this issue," he told reporters.
The latest changes mean the constitutional court can review the constitution or changes to it only on procedural grounds, not on substance, and scrap all decisions of the court made before 2012.
Despite Barroso's warning, there is little the EU can do to rein Orban in. Beyond political pressure, the EU executive can start legal proceedings but the process is onerous and unlikely to yield quick results.
In the EU, where political decisions are taken by consensus, pressure could mean isolation, weakening Hungary's voice in policy discussions. But Orban said he was not concerned.
"You are not guests of an isolated nation today," he told the more than 100 reporters who attended his news conference.
Accusing his EU critics of generalising, he said Hungary would suffer no consequences from any EU displeasure.
"We don't have a feeling that we are victims... I am absolutely optimistic about the Hungarian economy and Hungarian political life. We are not victims. Do I look like a victim?" he said. "We will win, I am sure about it."
Orban has said his government had the right to use its two-thirds majority in parliament to overhaul a constitution that it calls a hangover from the communist era.
Brussels disagrees. Many European leaders are concerned inadequate democratic norms in some countries in eastern and central Europe could undermine the fabric of the bloc.
Speaking after Thursday's meeting, German Chancellor Angela Merkel said a parliamentary majority should not be "abused". .
"(It) should be treated very carefully," she told reporters.
In Berlin, the EU's justice commissioner Viviane Reding said the Commission had the means to enforce its views.
"The Commission will examine Orban's constitutional changes and their consequences," she said. These could, she said, include cuts in EU payments to Hungary or restrictions on its voting rights.
"You don't play around with the constitution. You can't go and change the constitution every six months," Reding said. (Additional reporting by Annika Breidthardt in Brussels and Gareth Jones in Berlin; Editing by Paul Taylor)