The 2004 Olympic Games that officially open Friday in Athens have been surrounded by unprecedented security measures. The cost of security has reached $1.5 billion, four times that of the 2000 Olympics in Sydney. The massive operation involves a huge police and military presence and sophisticated technology aimed at warding off any terrorist attack.

The reason for such a large security operation is that these are the first Summer Olympics to be held since the September 11, 2001, terrorist attacks against the United States. Greek officials say those attacks motivated them to change their planning and double the original security budget.

Athens Mayor Dora Bakoyannis says that, despite international concern about possible terrorist attacks during the games, there has so far been no intelligence indicating that such attacks will occur.

"Greece and Athens have never been threatened," she stressed. "The Olympic Games have never been threatened, but they are still the biggest international endeavor which takes place in this new, unstable world."

Even though Greece has traditionally close ties to the Palestinians and Arab states, there are fears that Islamic militants might try to attack the teams of countries involved in the occupation of Iraq.

So, Greece has mobilized 70,000 police and military personnel, one half of its security forces, to provide protection for the Olympics. It has set up an air defense shield around Athens that has been boosted by the presence of NATO surveillance aircraft, which can monitor up to 500 kilometers of Greek airspace and pass information on any threat to a command and control center on the ground. Patriot missiles are in place near the Olympic village to shoot down any hijacked passenger jets like the ones that carried out the September 11 attacks.

Special precautions have been taken to protect the port of Piraeus, where several cruise ships are serving as floating hotels for visiting dignitaries. NATO warships are monitoring sea traffic in international waters near Greece. The alliance has also assigned its anti-biochemical warfare task force to Greece to deal with any potential unconventional attack. And it has put 400 U.S. special forces on alert in Germany to fly into Greece in case of a major security threat to the games.

The presence of NATO and of security guards accompanying several Olympic delegations is a sensitive issue in Greece, which has asked foreign personnel not to carry weapons in Athens. NATO spokesman James Appathurai, says that, when it comes to the chain of command, it is the Greeks who are running the show.

"This is a massively complex security operation involving, of course, a huge array of countries, all of which are coming with their own security details, but, also, specific countries and NATO have been engaged to provide security," he explained. "So, yes, there is some diplomacy. There's a lot of security, but, again, it's the Greeks doing the choreography. Greece is in charge. This is absolutely a Greek lead and a Greek security operation."

It is not just police and troops on the ground that are providing security. There is also an elaborate system of surveillance and tracking cameras that are supposed to spot suspicious activity and give early warnings to the command and control center. The system includes a dirigible loaded with cameras and recording devices that floats above the city. Some Greeks are uncomfortable with the police having computer-enhanced eyes and ears and have protested what they say is an invasion of their privacy. Others, like Athens University professor Theodore Couloumbis, say the system is counterproductive.

"If you feel that you live in a brave new world and that you have given up your freedom in order to get your stability and your security, then the terrorists have managed their one key objective: to rob us of our democratic values," he said.

But Mayor Bakoyannis says that is not happening.

"It's a price we have to pay. There is no other way," she said. "We are not thrilled with it. I don't think that any city in the world would be thrilled with that. But we know it's necessary. So we live with it."

The mayor says that the guns and the airship will be forgotten when the games get under way. And she says athletes and spectators should have nothing to fear.

"I believe that you are probably in the most secure place you can be during August 2004," she said.

Greeks and visitors alike hope that she is right.