"Clear," the leader yells as the group searches one room and then storms to another. Constant gunfire comes from just over a knoll.
The raid is a drill. The shooting is target practice. The intensity is because of the Olympics, now less than a year away.
In no other modern Olympiad - not even those held just after the world wars - has so much money, so many international resources and so much planning been invested in trying to anticipate and prevent attacks.
The Games are coming home to a city struggling under a colossal task: protecting the first post-Sept. 11 Summer Games even as terrorists increasingly display their mobility and might in places such as Baghdad, Bombay and Jakarta.
Greece, which the U.S. State Department branded one of Europe's "weakest links" against terrorism just three years ago, has shown signs of shedding its lightweight reputation. The stakes are too great.
Seven nations, including the United States and Israel, are helping Greek authorities with the security blueprint. Special anti-terrorism units - like the one practicing assaults on the outskirts of Athens - are undergoing intensive training never before imagined in Greece, including dealing with chemical and biological attacks. Subway cars may be outfitted with supplies of protective masks.
Meanwhile, 19 suspected members of the Greek terrorist cell November 17 are on trial in a special bunker-style prison courtroom. The apparent downfall of the once-elusive urban guerrillas last year was a huge relief for embattled authorities. The group is blamed for 23 killings since 1975, including U.S. officials, Turkish diplomats and a British defense attache.
"No one should be mistaken, the security effort for Athens 2004 is on track even as we face tight schedules and tremendous challenges," said Peter Ryan, the former head of security at the Sydney Games in 2000 who now advises Athens planners.
Any misstep, however, could be costly with Athens' preparations on such a tight timetable.
A U.S.-led consortium is still awaiting the final green light from Greek officials to move ahead with its $280 million security contract, which includes construction of a central command and communications network.
The delays have snagged other key elements in the record $600 million security package: a planned network of surveillance cameras, dry runs for special units and other measures. Security issues could dominate the next inspection visit to Athens in October by International Olympic Committee overseers.
Geography worries Olympic planners. Greece is a key European Union destination for illegal immigrants mostly from the Middle East and Asia. Tougher border patrols have been imposed, but the human traffic continues at the rate of thousands each year.
Terrorism experts say it's unlikely that al Qaeda operatives or others have used the illegal immigrant networks as avenues to Europe, but that could change if normal routes prove too risky.
"Terrorist groups seek the path of least resistance," said Charles Pena, a defense and security analyst at the Cato Institute in Washington. "If illegal means prove easiest, then that could become something of big concern for the Olympics ... 9-11 showed it's a new world."
One that is quickly stripping any vestiges of innocence from the Olympics. Scenes from past Games - such as athletes wandering Rome's historic center in 1960 or freely sightseeing in Los Angeles in 1984 - now are seen as inviting disaster.
At least 100 security agents will accompany the U.S. team to Athens as part of a $2.7 million special State Department security package, said U.S. officials. Some other nations, including former Olympic host Australia, are also considering bringing private security or restricting athletes to their venues and the Olympic Village.
"Security is an unwelcome fact of every Olympic Games now," said Simon Clegg, president of the British Olympic Association.
This is what unnerves security officials the most: the inability to predict where - or even how - the next terrorist strike will be waged.
"Frankly, if you used Sydney as an exact blueprint for Athens you'd be missing one extremely important variable and that was 9-11," said Thomas Miller, the U.S. ambassador to Greece. "You got to be flexible. You got to be willing to adapt to the changing threat."
Miller called the countdown to the Games the "crunch" for security planners.
"What happens over the next year is really what matters," he said.
Amid the preparations for the worst, there is one detail impossible to assess: Just how much threat does terrorism pose to the Games?
A serial bombing suspect is charged with the 1996 blast during the Atlanta Games that killed one person and injured 100. Sydney and Salt Lake City in 2002 passed unscathed. The 2002 World Cup inJapan and South Korea - the world's other main sports showcase -
also was spared.
"But you still must remember that for a terrorist from a group like al Qaeda, the Olympics could be considered one of the crown jewels to embarrass the West and impress their backers," said Bruce Hoffman, an international terrorism expert for the Rand Corp. in Washington, who also advised on the Sydney Games.
"The Olympics could be seen, through their eyes, as an establishment event closely associated with the West," he added. "There is no room at all to be complacent."
By Brian Murphy