"Foreigners will never buy arable land here, no matter what they decide in Brussels," national news agency MTI cited Orban, a former prime minister, as saying. "I am committed to defending Hungarian land."
If implemented, his pledge could put Budapest at loggerheads with its European Union partners and ultimately lead to it being taken to the European Court of Justice for obstructing the free movement of capital - a key EU treaty principle.
Hungary's 2004 accession treaty barred land purchases by foreigners until 2011 in an effort to prevent wealthy European investors from buying up large chunks of arable land in the poor new member state. Similar transition clauses were negotiated by other ex-communist newcomers such as Poland and the Czech Republic.
Agriculture accounts for only 4.3% of Hungary's gross domestic product but the land issue touches an emotional political nerve in a landlocked country that endured foreign domination and has deep agrarian traditions.
The far-right party Jobbik, which polls show might become the second-biggest political force after Fidesz, garnered much of its support by calling for a renegotiation of the accession treaty and blocking foreign land purchases for good.
The Hungarian parliament passed a resolution in February, one of its last acts before plenary sessions ended ahead of the elections, authorising the government to negotiate a two-year extension to the restrictions with the European Union.
But Orban said the EU had little say over the matter.
"The future of the Hungarian land depends not on the decision in Brussels," he said. "[It depends] only on us."
Even the ruling Socialists, expected to be heavily defeated, mentioned the issue in their election manifesto.
"We will continue to protect our most important national property and treasure, the land," the programme said, without further specifics.
Fidesz, in power between 1998 and 2002, considers the issue especially close to heart, and its current election programme singles out agriculture as a key vector for economic recovery.
While in office, the party took a hard line on foreigners' land purchases that had become widespread, especially along the western border with Austria, which ruled Hungary as part of the Austro-Hungarian Empire until the end of World War One.
Orban said in 2001 that up to a quarter of Western Hungary's farms were effectively owned by Austrians, many of whom used Hungarian intermediaries to buy land.
"Every Austrian farmer who bought land in Hungary should feel pleased to have got away with it," Orban said then.
(EurActiv with Reuters.)