Thousands of financial staff across Europe will be working flat out during ``Euro Big Bang'' weekend, converting the prices of European shares and bonds into euros and reprogramming computers to cope with the switchover.

``From a financial standpoint, this start of a new currency is the biggest single event we will have seen in our lifetime,'' said a partner Paul Cantwell at Andersen Consulting. ``It's like watching the Berlin Wall coming down.''

For months, financial employees throughout Europe have been sacrificing weekends to do mock runs for the conversion marathon from December 31 to January 3.

The starting gun will be fired on New Year's Eve when finance ministers fix the rate at which the euro will trade. Staff will then be racing against the clock to translate the value of securities from the 11 countries inthe euro zone into the new currency in time for when markets open on January 4. That's when brokers will have to be ready to deal in euros.

``This is a massive logistical exercise. Nothing has ever been attempted on this scale,'' said Roger Bates, who is coordinating the conversion for Deutsche Bank in London.

London, Europe's biggest trading centre for currencies and foreign shares, will be at the heart of the action even though Britain is not expected to join the euro until at least 2002. Up to 30,000 employees will be working in the city, London's financial district, a tenth of the normal work force.

The stakes involved in ensuring the transition goes smoothly are huge. Problems making the changeover to the euro could cost financial institutions clients and money.

The switchover requires military-style planning. Many institutions have set up ``war rooms'' and ``command posts'' to coordinate their activities over the long weekend. Flow charts line walls and mobile phones proliferate.

``In a way,we're looking forward to it,'' says senior vice-president Meager at Salomon Smith Barney. ``We've done all the revision. Now we want to do it for real. The Adrenalin will be pumping.''

Staff will be able to snatch a few hours' sleep in nearby hotel rooms booked months in advance, cappuccino trolleys will ply hallways to keep the bleary-eyed awake and caterers will bring in plenty of food.

``You'd be surprised how many people have opinions on sandwich fillings,'' Meager joked. In fact, staff at one brokerage house grumbled about being served ready-made dinners during the trial runs and won assurances that their new cafeteria would be up and running during the big weekend to serve gourmet meals.

The nearest equivalent to conversion weekend, market watchers say, was the dramatic 1986 deregulation of the London Stock Exchange, which was also known as the Big Bang.

Then there was trouble when computers seized up and thousands of trades were unsettled months afterward. ``There was a logjam of paper andsome back offices effectively glued up,'' said Andersen Consulting's Cantwell.

While the big institutions say they are ready, they say they are not sure everyone else is -- especially the smaller players -- and that is what could cause things to snarl.

``It's like a grand opera but everybody has been practising in a different room and there is no conductor,'' said Cantwell. ``Nobody knows how it will be when they have to sing together.''

In addition to dealing with the conversion, there will be the normal year-end housekeeping in which a whole 12 months worth of accounts will have to be finalised.

One of the first signs of things going wrong will be if one bank's calculations fail to tally with those of a trading partner's. Staff on both sides will have to scramble to find out the root of the price discrepancies.

Differences in simple rounding of figures could produce confusion. ``You could see companies having trouble in translating from the old currencies into new,'' said Cantwell. ``They alsohave to convert all their price histories...There may be some people who won't be able to finish in time.''

Central bankers have made emergency plans in the event of any massive payment problems or computer systems breakdowns. But most financial institutions have scaled down the amount of business they transact to make the conversion process easier.

While the weekend will be critical, bankers say it could take weeks and possibly months for it to be ``business as usual.'' ``We expect the load on back offices to be very intense during the weeks following as they try to handle the extra paperwork,'' said Cantwell.

Although institutions' ability to navigate the post-euro environment will be key to their future, they're expected to bury their rivalry during the highly charged transition period.

``It's no use being an island of perfection,'' said PierreAnson-Tsang, an EMU manager at Dresdner Kleinwort Benson. ``It's in all our interests to get it right.''