Published on Sunday, the survey said that more than half those asked thought the state should prevent the Basque premier Juan Jose Ibarretxe from going ahead with his plan for a referendum.
The Spanish parliament overwhelmingly rejected last week Ibarretxe's plan for Basque "free association" with Spain.
In response, Ibarretxe called early regional elections for 17 April and vowed that if he won, he would call a referendum on his proposal for the northern region, which has seen decades of separatist violence.
A referendum without the blessing of the Spanish parliament would be a major affront to Prime Minister Jose Luis Rodriguez Zapatero, whose Socialist government has sought dialogue with the Basques.
More than 62% of Spaniards think the government should launch a legal challenge if Ibarretxe goes ahead with his pledge to call a referendum, according to a survey of 800 people by pollsters Sigma Dos in El Mundo newspaper on Sunday.
If Ibarretxe pushes ahead with a referendum after the courts ruled it illegal, just over 50% said Madrid should ban it "even if it had to resort to the security forces".
The number of Spaniards supporting these options had climbed sharply in the past month, El Mundo said.
The margin of error of the poll, conducted in the two days after the parliamentary debate, was 3.35%, it said.
ETA seeks an independent state
from Spain and parts of France
Under pressure from the opposition Popular Party to take a tougher line on the Basques, Zapatero has to tread a delicate line to avoid alienating regional allies in wealthy Catalonia who are also demanding more autonomy from Madrid.
Zapatero's Socialists lack a majority in the national parliament and depend on regional parties to get their legislation through.
Political developments in the Basque country are set against the backdrop of violence by armed separatist group ETA.
ETA, branded a terrorist group by the European Union and the United States, has killed some 850 people since 1968 in a campaign for an independent state carved from northern Spain and south-western France.