COPENHAGEN, Denmark (AP) _ The Brogaards are fairly content in retirement _ mortgage paid off, children grown and moved away, their combined social security bringing home nearly $1,000 a month.

But Svend Brogaard says he has started to worry since he read leaflets warning that things might get a lot worse if Danes vote in a referendum Thursday to join Europe's monetary union and replace their 125-year-old krone with Europe's new currency, the euro.

``When I hear that the pension _ the one that the Danish state is paying to people who worked hard all their life _ could be threatened because of the euro, it makes me think twice,'' Brogaard says.

The 73-year-old retired salesman says he's voting no, as will many others of the 4,004,679 eligible voters. But opinion polls published Monday and Tuesday forecast a virtual tie, after months of giving the anti-euro camp a slight but consistent lead. The undecided vote remained high, at up to 12 percent.

A rejection, say the nation's leaders, will leave Denmark on the sidelines of the new, borderless, single-currency Europe that is becoming more of a reality day by day. If it won't join the euro, the leadership warns, it won't have enough say in Europe's big decisions, and its currency will be too weak to withstand onslaughts by speculators.

But the opponents of the euro have skillfully played on a much more tangible fear: the notion that the treasured social security system is at stake. Danes uncomplainingly pay some of the highest taxes in the world _ 50 percent of their gross domestic product _ to maintain free medical care, education from kindergarten to college, generous unemployment pay and long parental leaves.

The 'no' camp claims Denmark will lose its freedom to set its own taxes because it will be locked into the euro and the European Union's plan to harmonize taxes. It says countries that favor high-tax, high-welfare systems, and those that favor the opposite, will all be squeezed into a one-size-fits-all policy set by the European Central Bank in Frankfurt, Germany.

Little Denmark by itself may not matter all that much in the big picture of a drive for continental unity that grew out of the wreckage of World War II. Its economy is small alongside the big Euro-boys, France, Germany and Italy. But its vote is being closely watched by other powerful neighbors, Britain and Sweden, both of which have opted out of the euro for now.

They too will have to hold referendums at some point, and a 'no' vote in Denmark is sure to invigorate the anti-euro campaigns elsewhere.

The euro's steady slide against the dollar _ 27 percent since it was introduced into world trade in January 1999 _ doesn't help the 'yes' camp.

The new currency, which isn't in public circulation yet, but is already posted on menus and in supermarkets in the 11 European countries that have signed on (Greece becomes the 12th on Jan. 1). Coins and bills go into circulation in January 2002, and if Denmark votes yes, its currency will be replaced by a euro that still carries its queen's face, but phases out a currency Danes have been using since 1875.

``The euro is our future. One big market with one currency makes life simpler for all of us,'' said 51-year-old Else Vissing, a clothing store worker. ``By standing outside, we'll really be a small economy next to a huge one, and that can't be good for the krone.''

Some Danes worry about more than just money. They see EU membership is an erosion of Danish sovereignty, as more and more powers are ceded to EU headquarters in Brussels, to dictate all sorts of everyday matters from the brightness of taillights to the bacterial content of cheese.

``The euro is another step toward less democracy and more union with decisions taken in Brussels or Frankfurt and not in Copenhagen any more,'' said 59-year-old Per Nordbo.

But it's welfare that is giving Prime Minister Poul Nyrup Rasmussen and his left-center government the most trouble in its campaign to win a 'yes' vote Thursday.

Last week Danish media reported that he had gone as far as to consider asking his European partners for a written guarantee no change would be forced on the social services. Some Danes ridiculed the idea, and Nyrup Rasmussen said he had dropped the idea.

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On the 'Net:

Danish foreign ministry's site: http://www.um.dk/english/

European Union's Euro site: http://europa.eu.int/euro/html/entry.html