But given Istanbul's grim record of terrorist attacks, the proximity to Iraq, and the presence of US President George W. Bush and other leaders, officials are fearful of the slightest security lapse.

"Security is factor number one for this summit. There must be zero errors," said Umur Apaydin, head of the committee organizing the July 28-29 meeting.

All traffic will be banned within a perimeter of 10 kilometers (six miles) around "NATO valley" in the heart of Istanbul, along with the main 20-kilometer highway to the airport.

The advice on the summit hotline set up by the Istanbul city government? "Wear good shoes and leave earlier for work."

NATO valley is on the European side of Istanbul, in the midst of the busy modern quarters of the city, and includes two major highways, the closing of which is likely to cause inextricable traffic jams.

The governor of the city, Muammer Guler, says there is no serious threat of terrorism.

But in a vast metropolis, where more than 60 people lost their lives in attacks last year, and where there are known to be extreme leftist, Kurdish and radical Islamic networks, police and armed forces are taking no chances.

Arrests have been stepped up, and police in recent weeks have announced the detention of at least 13 suspected members of Ansar al-Islam, a militant Kurdish group in northern Iraq that the United States says is associated with Al-Qaeda. They were suspected of plotting attacks during the summit.

Authorities are determined to prevent a repetition of the November car bomb attacks on two synagogues, the British consulate and a British bank which killed 63 people and injured hundreds of others.

All motorized traffic, with the exception of official vehicles and shuttle buses, will be banned from the security perimeter. All people who live or work in the zone have been checked and all their movements will be controlled at checkpoints.

"The police came round to verify our identities," said concierge Salih Kucuk, 42. "They were making checks to install snipers on the roof."

According to the press, more than 300 people have been detained and questioned in recent weeks, including Islamists and leftists but also journalists and members of Kurdish cultural associations.

For 10 million people living outside the zone, the disruption is likely to be enormous because the traffic restrictions in NATO valley are expected to spill out all over the city.

"Television has spoken of nothing else for several days," said taxi driver Mehmet Bostan, 46. "I think people are going to take advantage of the situation to take a break. Otherwise, I advise them to walk."

Making the situation worse will be the fact that the circulation of vehicle ferries between the European and Asian sides of the city will also be banned, and all traffic will be diverted to the two bridges across the Bosphorous, which already are at saturation point.

Shipping carrying fuel or dangerous products has been prohibited from passing through the Bosphorous and so, to the annoyance of fishermen, have all fishing boats.

"We are already going through a crisis, and now they are telling us not to go to sea for four days," said fisherman Huseyin Teksen, 53. "The only word these leaders have in their minds is security. Well, if they are so afraid of getting killed, they only have to stay away."

Behind the barrier of metal and concrete sealing off NATO valley, some 3,000 delegates from the 46 nations invited will be under the protection of 23,000 police officers and units from the armed forces, including specialists in biological, chemical and nuclear weapons. All flights over the city will be banned, except for NATO warning and control planes that will patrol the skies round the clock during the meeting.

In addition, 3,500 journalists and 35,000 service workers have been given accreditation for the summit.

As a final precaution, each head of delegation will be supplied with a bullet-proof limousine.

And the government has said it will permit no demonstrations against NATO except in a few designated areas far from the conference center.

WAR.WIRE