(Corrects first name of prosecutor in paragraph 7)
* Prosecutors: suspect driven by nationalism, anti-Semitism
* Suspect "planned to blow up vehicle bomb in capital"
* He assembled arsenal of explosives, guns, detonators
* Report says suspect copied Norwegian mass killer Breivik
By Dagmara Leszkowicz and Marcin Goettig
WARSAW, Nov 20 (Reuters) - Polish officials said on Tuesday they had arrested a radical nationalist who planned to detonate a vehicle loaded with four tonnes of explosives outside parliament, possibly when the president and prime minister were in the building.
The suspected plot was the first of its kind to be exposed since Poland threw off Communist rule more than 20 years ago. It is likely to put intense scrutiny on radical right-wing groups in Poland which are fiercely opposed to the liberal government.
Polish television, citing sources close to the investigation, said the suspect planned to copy methods used by Anders Behring Breivik, who killed 77 people in bomb and gun attacks in Norway last year and said he was driven by far-right views.
"The case looks very serious," Pawel Gras, a government spokesman, told a local radio station. "We know that the possible targets were to be the president, the parliament and the government."
Prosecutors said the man, a scientist who works for a university in the southern city of Krakow, had assembled a small arsenal of explosive material, guns and remote-controlled detonators and was trying to recruit others to help him.
A video recording taken from the suspect showed what prosecutors said was a test explosion he conducted, sending up a huge cloud of dust and leaving a large crater in the ground.
"The suspect does not belong to a political group or party. He claims that he was acting on nationalistic, anti-Semitic and xenophobic motives," prosecutor Mariusz Krason told a news conference.
"He carried out reconnaissance in the neighbourhood of the Sejm (parliament). This building was to be the target of the attack. He collected explosives and materials for detonation," Krason said.
Polish society is deeply polarised between liberals and those who believe the country is neglecting its Catholic roots and succumbing to foreign influence.
Most right-wing groups renounce violence, but some on the margins are more radical. A rally in the capital, Warsaw, this month by right-wing nationalists turned violent, when youths in the crowd started throwing flares and stones at police.
Prosecutors produced evidence suggesting the unidentified suspect was planning a sophisticated attack.
They showed reporters photographs of pistols and bags of ammunition which they said he had bought in Poland and in Belgium. They also showed several vehicle licence plates, both Polish and foreign, which they said had been found among his belongings.
They said the suspect had used his scientific background to assemble the explosives himself. "He is a specialist in the field," prosecutor Krason said.
Officials said that they had found explosive substances including hexogen and tetryl, as well as detonators that could be triggered remotely using a mobile telephone.
The dean of the Agricultural University in Krakow, where prosecutors said the arrested man worked, said the man had never given any reason for suspicion.
"It never occurred to us that at our school there could be a person involved in such matters. There were no indications from his co-workers that anything unusual was happening," Roman Sady said. (Additional reporting by Wojciech Zurawski in Krakow; Writing by Christian Lowe; Editing by Louise Ireland)