Tim macy was standing 100 m from the bomb when it exploded. Many of the revelers at Atlanta's Centennial Olympic Park thought the boom and flash were part of the show, as the 10th day of the 1996 Olympic Games wound down. But Macy, the park's general manager, knew better. Now the venue manager at Sydney's Darling Harbour Convention and Exhibition Center (which will host five Olympic sports, including judo and boxing, during the 2000 Games), he recalls running toward the blast: "I saw a deep, smoking hole and about 70 people, covered in blood from the shrapnel, on the ground."

Ever since 11 Israeli athletes were killed by the Palestinian terror group Black September at the 1972 Munich Games, security has been an Olympic obsession. Sydney has been relatively free from the pre-Games threats and attacks that have plagued previous host cities. Says Australian Attorney General Daryl Williams: "Australia faces a low risk of any significant security incident." But terrorism is changing in ways that make it more dangerous and more difficult to counter. New South Wales Police Commissioner Peter Ryan, who has overall command of Olympic security, says there "can never be any guarantees. But we have planned for every contingency."

Ryan's confidence is widely shared. "They have the capability to cope with all potential threats," says Yoram Schweitzer, of Israel's International Policy Institute for Counter Terrorism, who met with Olympic security planners during a visit to Australia last year. But the Games may now be too large to be protected by one country alone. Says a U.S. security agent: "You need the cooperative assistance of the world to carry off these events."

Australia's politicians and law enforcement officials acknowledge their dependence on intelligence and training provided by overseas agencies. But they insist that Australia has full responsibility for the safety of all athletes and dignitaries attending the Games. Two private security contractors involved in the Olympic security effort told Time that Israel, the U.S., Britain, Germany, France, China, Indonesia, Japan, South Africa and Russia will be allowed to bring in weapons to protect their Olympic teams and vips. "The major countries that we deal with or that our forces train with, we're going to turn a blind eye to," says one contractor, "because we know they can toe the line." Williams says no such deals have been made: "Foreign security officials will not be given permission to carry firearms. And they will not be participating in the protection of anybody [at the Games]," he says.

Ryan says the 2000 Games will be the "safest ever." That promise was also made by Atlanta Organizing Committee for the Olympic Games chief Billy Payne. But the massive security effort in 1996 didn't stop a homemade pipe bomb from killing one and injuring 111 at Centennial Olympic Park. With instructions for making bombs from widely available ingredients published on the Internet, terrorist attacks are becoming more random-and harder to predict.

Religious fundamentalists who view violence as a "divine duty" are also making terror more lethal. The chief villain in this category is Osama Bin Laden, the alleged mastermind behind many of the most brutal attacks of the 1990s. Suspicions that Bin Laden has established terrorist cells in Australia were first raised in 1994, when the f.b.i. and the c.i.a. traced phone calls made by some of the convicted World Trade Center bombers from the U.S. to numbers in N.S.W. Australia's security chiefs refuse to expand on these allegations, or to be drawn on any specific threats to the Games. But they admit they are preparing for the full gamut of risks, including biological, chemical and nuclear incidents. Six years in the planning, the $A180 million Games protection project will be the largest peacetime security operation in Australia's history, involving 5,000 state police, 4,000 defense personnel, 4,500 private security guards and 3,500 volunteers.

But don't expect to see submachinegun-toting troops lining the streets, as they did in Seoul in 1988, says a senior federal government advisor: "Australia's culture means we don't want security in our face." Purpose-built Olympic venues such as the athletes' village provide a strategic advantage because security measures can be unobtrusively built in and monitored, says Police Commissioner Ryan.

Spectators may not notice the computer-controlled infra-red cameras, motion detectors and perimeter patrols-or see the U.S.- trained bomb-sniffing dogs that will search competition venues, or the Australian Navy divers who will examine ships' hulls. But Games organizers say people should arrive at venues at least an hour before events to allow time for "mag and bag" checks-bag searches and screening with magnetometers (metal detectors). Sydneysiders will also have to shed some of their sports-going traditions. "Don't even attempt to come in with a big Esky [drinks cooler] crowded with your stuff," says Ryan. And every spectator will be checked, he adds, including Olympic officials: "If that creates a political incident, hard luck."

While Australia's security forces have had few terrorist attacks to practice on, they have a counterterrorism blueprint, the National Action Terrorist Plan, drawn up after the 1978 bomb blast during a Commonwealth leaders' meeting in Sydney, which brought politically motivated violence to the island continent. Joint training exercises are routinely held and have intensified in the lead-up to the Games, says State Protection Group commander Norm Hazzard, whose unit responds to hostage sieges in N.S.W. "If an incident was to occur [at the Games], we are well rehearsed, so there'll be no red tape and no holdups."

That training includes knowing when to call in Australia's elite counterterrorist squads, like the army's Special Air Service, which will be on standby in four locations around Sydney during the Games. Says Australian Defence Force Academy lecturer Alan Thompson: "If you stage a hostage siege during the Games, you [will be] signing your own death warrant, because there is no doubt that the s.a.s. will take you out." But their role is "an absolute last resort," according to the Australian Defence Force's Brigadier Gary Byles.

Seven weeks before the Games, Sydney's security effort is "ready to go," says Ryan: "We are far more prepared than Atlanta was at this stage." But two security breaches at Sydney airport last month led to an urgent review and a security upgrade. Aboriginal leader Charles Perkins also sparked concerns in April when he predicted "burning cars and burning buildings" during the Olympics. While Perkins has since softened his stance, Ryan expects that there will be street protests against the Games. "We will allow them to take place peacefully, but not to hinder the Games or degenerate into violence," he says.

The anti-violence stance lies behind the government's declared no-guns policy for foreign security agents. Attorney-General Williams says Australian private security guards may be allowed to carry arms when protecting foreign athletes or dignitaries. But two private security contractors told Time countries that have strategic relations with Australia will be given free rein. "If we have a major incident and an athlete dies, we're going to have a really big problem if we go it alone," one says.