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With terrorism an ever-present threat, France is on a war footing to ensure security for 16 heads of state and as many as 1 million people attending ceremonies this weekend for the 60th anniversary of the D-Day (search) landings in World War II.

Surface-to-air missiles (search) poised to shoot down stray or enemy aircraft. More than 15,000 police and soldiers deployed to keep order. Stocks of antidotes ready in case of chemical attack.

The rollout of such military firepower and troops is among the largest ever since the more than 150,000 Allied forces stormed the Normandy (search) beaches code-named Sword, Juno, Gold, Omaha and Utah on June 6, 1944, in a momentous military bid to liberate Europe from Adolf Hitler's grip.

Ensuring security for such a gathering of world leaders, Normandy residents, war veterans and visitors is a major headache at a time of terror threat.

"We have to think about it, not take it lightly and do everything to lower the risk to zero," said Patrick Jardin, mayor of the Normandy town of Arromanches, where a ceremony for heads of state is planned.

"The advantage of such a ceremony is that there will be a deployment of forces so large that we'll feel secure. But that can give ideas (to terrorists) — and we're aware of that," Jardin said.

Cars will be stopped at checkpoints along a 60-mile stretch of Normandy coast, and drivers without special passes will be turned away, said Defense Ministry spokesman Jean-Francois Bureau.

Military helicopters, Mirage fighters and Crotale surface-to-air batteries are authorized to escort, and if necessary, shoot down, any unidentified aircraft that enter the area.

Among the heads of state expected are President Bush, French President Jacques Chirac and Queen Elizabeth II of Britain. Chancellor Gerhard Schroeder and Russian President Vladimir Putin will represent their countries on D-Day for the first time.

Organization gets even trickier because many of the foreign dignitaries are bringing their own security teams.

In Paris, police will block off a large swath of the city — including the presidential palace, the Champs-Elysees, the U.S. Embassy and Les Invalides. A protest against the Iraq war is scheduled for Saturday outside the zone as Bush arrives.

Paris police have also asked museums, cinemas and stores to be on high alert and check handbags of incoming patrons.

In Normandy, the military has set up a temporary air base near Caen. Regional health officials have stockpiled antidotes in case of chemical attack and airliners will be banned over the area.

Hundreds of police were being mobilized in case of a terror attack, and hundreds more were to join convoys that contain the heads of state, though the Defense Ministry says it has no intelligence information indicating a terror attack is likely.

On Monday, police patrols with sniffer dogs and hand-held metal detectors fanned out on the ceremony sites near Arromanches and Omaha Beach, while troops armed with automatic weapons patrolled railway stations.

Hospitals have asked all their staff to be on hand, and paramedics were instructed to be ready for anything from scraped knees to bomb attacks. Nuclear, biological and chemical weapons experts have also been readied.

Authorities on Tuesday raised France's terror alert status from "orange" to "red" — the second-highest on a four-point scale. Police will step up identification and baggage checks on trains, especially those headed to Normandy, and water will be checked and stocked.

Special vehicle stickers have been distributed to Normandy residents, who authorities are encouraging to stay home to watch the ceremonies on TV instead of trying to rubberneck at dignitaries.

The country has mobilized 9,000 soldiers, equipped with AWACs surveillance aircraft, unmanned drones and naval minesweepers, the Defense Ministry said.

About 6,000 gendarmes — members of a unique French police force that falls under the Defense Ministry — are to check vehicles, smooth traffic and manage crowds if any protests get out of hand.

About 20,000 people, including 8,000 veterans, are to attend many of the 16 official ceremonies in Normandy from Saturday to Monday, the Defense Ministry said. Some 3,500 journalists are accredited to cover the event, and as many as 1 million people are expected for a series of other commemorations around the region, the Interior Ministry said.