The European Union threatened today to take France to court if it does not lift its embargo against imports of British beef. The threat came on the eve of an important summit meeting here of the 15-nation free-trade bloc.

The European Commission declared in 1998 that British beef was safe to eat, attempting to put to rest the 1996 "mad cow disease" scare. But France and Germany have refused to lift bans that technically are illegal under European law.

Monday, the French food safety agency ruled that British beef still could not be guaranteed free of a disease called bovine spongiform encephalopathy, or BSE, which has been blamed for a similar fatal brain-wasting disease in humans. Wednesday evening, the government of Prime Minister Lionel Jospin decided unanimously to maintain its ban.

"It's not a protectionist measure. It's a problem of health," said European Affairs Minister Pierre Moscovici. Because the ban is based on a ruling by the food safety agency, "we could not do otherwise," he said.

The German government has said it will lift its embargo. It does not seem to be in a hurry, but its ban has not earned the same kind of British anger as the French ban.

France long has been Europe's strongest believer in the European Union, insisting a united Europe is the best way to stand up to the United States on the world stage. But while member nations have occasionally violated EU dictates in the past, few have done so as long as France has in the beef case.

British Prime Minister Tony Blair said today: "You can't have a situation where people pick and choose what rules of the European market to obey. It's a decision the French government has taken and they will have to face the consequences of that."

Next week, French President Jacques Chirac is scheduled to open the new building of the European Parliament in Strasbourg, France. British Parliament members are threatening to boycott the ceremony.

David Byrne, the European Commission's health minister, said France had five days to respond to a commission proposal to lift the ban. After that, he said, "if the embargo isn't lifted we are straight into court."

A case in the European Court of Justice could take years.