Europe's biggest and longest peacetime security operation went into force on Sunday when "no go" areas were imposed in Athens for the Olympic Games starting in mid-August.

The measures, which dwarf any previous in Europe because of the need to sustain them for the entire month of August, were clamped on the Greek capital even though the U.S. admiral overseeing NATO involvement said the Games threat so far was "benign."

With hundreds of athletes already arriving in Athens for the world's largest sporting event, one newspaper warned Athens residents that the August 13-29 Olympics would turn their lives upside down.

"The No's of August," the Eleftherotypia newspaper called the security measures and traffic restrictions that will reach into every corner of the city of four million.

Greek organisers have spent three times the amount for the last Olympics in Sydney, to guard the Games with the fallout of September 11, 2001 attacks and Iraq hanging over them.

NATO, Patriot missiles, anti-chemical warfare experts, submarines, frogmen and up-to-date surveillance equipment will be at the disposal of a 70,000-strong military and police force.

"This is the biggest operation by the Greek armed forces since World War Two," said Army General General Vassilis Giannopoulos. "We've planned for everything."

As well as guarding venues, troops will be stationed at power stations, waterworks, tunnels and bridges.

PLANE IN SKY IN ONE SECOND

"We can have a plane in the sky in one second," Giannopoulos said of the air cover for the Games.

Some 1,200 surveillance cameras have been deployed throughout the city.

Frogmen will guard cruise ships, including the world's largest, the Queen Mary II, where many VIPs will stay.

In an interview with the Washington Post, Admiral Gregory Johnson said there was no specific intelligence information signalling a possible terrorist attack on Athens.

"There's sort of a baseline hum you get in certain areas of terrorist activity," said Admiral Johnson at the Naples headquarters of NATO's southern Joint Force Command which is contributing ships, planes and chemical warfare experts.

"(In the caee of Greece) the noise level, shall we say, is pretty benign right now, and I just don't see any spikes."

But he warned there should be no complacency.

"We don't want to be too comfortable. There could be something deeply buried we just haven't seen or anticipated."

World leaders planning to visit the Olympics include British Prime Minister Tony Blair and French President Jacques Chirac. Former U.S. President George Bush is also due to attend.

Greek newspapers said that as well as the official force, a "private army" of security consultants would be on hand to protect VIPs.

"Foreign security companies operating in Iraq have won huge contracts to protect business leaders and others from the United States and other nations," said the Ethnos newspaper.

What has been billed by some as a "month of torture" for Athens residents began when the first vehicles took to the streets with one lane of main streets closed for the exclusive use of Olympic vehicles.

Newspapers warned the lane closures would test the patience of Athenians to the limit and could turn residents against the Games before they even started.

Chief Olympics organiser Gianna Angelopoulos said Athens was ready to put its best foot forward after years of criticism over delays in construction of venues and other preparations.

"Everything humanly possible has been done," she told the Kathimerini newspaper in an interview. "We have made up for lost time at the start and are ready for the last sprint."