By Annika Breidthardt

MUNICH, June 9 (Reuters) Fans were urged to turn up three hours early for the first match of the 2006 World Cup today as German officials welcomed partying crowds but warned they would not ''joke around'' with security.

''Everyone can come, shout until they lose their voices, have a great time and feel at home with friends,'' said Rainer Riedl, interior ministry spokesman in the Bavarian capital Munich where Germany and Costa Rica kick off the tournament at 1600 GMT.

''But the message to any hooligan or trouble maker is clear -- security will function and we are not here to joke around.'' Fans arriving for the opening game of the world's greatest sporting event will pass through a double ring of security -- a police check on the approach to the stadium and a ticket check at the entrance.

Tickets for the entire tournament are personalised, each one bearing the buyer's name, in a special measure designed to boost security and stamp out black market trading.

But it was unclear what proportion of the 64,700 fans streaming into Munich's newly built, 340 million euro (430 million dollars) stadium would have their passports and ID cards checked against the names on their tickets.

Stewards ''will probably run spot tests rather than check every single one,'' police spokesman Gerhard Schmitt said. ''That would just take too long.'' German officials have terrorism and hooliganism uppermost in their minds as they try to protect the month-long tournament without stifling it with security.

Security officials say that although there is no evidence of any concrete militant plans, there is a general ''abstract risk'' of an attack. They see the opening match and the July 9 final in Berlin as the most symbolic, and therefore attractive, targets.

Munich witnessed one of the most traumatic events in the history of sport when Palestinian militants massacred 11 Israeli athletes at the 1972 Olympic Games.

Authorities have imposed a no-fly zone with a radius of 56 km (35 miles) around the stadium for the opening game.

NATO's joint fleet of AWACS radar aircraft based in Germany and Britain was poised to start patrols that will run throughout the World Cup finals.

''The first flight for us will be today,'' said a spokesman at the AWACS base near Aachen in western Germany.

A single E3-A aircraft at 30,000 feet can detect a hostile aircraft at any altitude from more than 360 km (200 nautical miles) and direct German fighters to intercept it.

The security net involves 250,000 police on duty around the country and a comprehensive intelligence-sharing network with a round-the-clock unit in Berlin at its nerve centre.

But the fans already appeared to be enjoying themselves.

German and Costa Rican colours dominated Munich's central Marienplatz square, where soccer anthems were blaring out and a large screen has been set up for those without a ticket.

''This is a once in a lifetime experience,'' said a fan from Kiel in northern Germany, wearing a black-red-gold hairpiece and tucking into white sausages and a beer.

''We don't actually have a ticket but just being here is going to be worth it,'' said his wife in a Costa Rican shirt and wearing a Brazilian scarf.

REUTERS DH HT1835