The London Olympics will open just over a year from now, amid the stunning and historic backdrops of the Houses of Parliament, the Tower of London and Buckingham Palace - all the monuments that make this one of the world's most popular destinations.

For that very reason, these games will have a security presence like no other in the face of a constant terrorist threat.

Wednesday (July 27) marks the one-year countdown to the opening ceremony on July 27, 2012. Next summer, London will be welcoming 10,500 athletes from more than 200 countries and regions, 5,000 officials, 20,000 media personnel and hundreds of thousands of visitors for a 17-day extravaganza featuring 26 sports in 32 venues.

"With a year to go we can safely say we are ready to welcome the world," London Mayor Boris Johnson said.

Venue construction is largely completed, tickets are almost sold out, and the government says the games will come in under the 9.298 billion pound ($15 billion) budget. The Olympic Park is changing the face of a previously rundown area of east London.

Athletes will be competing in iconic venues and locations across the capital.

Fans will see Usain Bolt sprinting down the track in a new 80,000-seat Olympic Stadium, beach volleyball players dueling on the sand in Horse Guards Parade, triathletes splashing in the Serpentine in Hyde Park, Roger Federer and Rafael Nadal stepping back onto Centre Court at Wimbledon, archers firing their arrows at Lord's cricket ground and showjumpers clearing fences at Greenwich Park.

Underpinning the sports festival will be one of the biggest security operations ever mounted.

Security at the Olympics has been a critical issue ever since the 1972 Munich massacre, even more so after the September 11, 2001 terror attacks. A day after London was awarded the games in 2005, suicide bombers attacked London's transport network, killing 52 people.

The British government is planning for the national terror threat to be "severe" during the Olympics, meaning an attempted attack is highly likely. Security screenings for spectators will be tight and widespread, with airport-style checks at most venues. Away from the competition sites, protecting the Underground subway network and public places will be a major challenge.

"We're already seeing chatter from terror groups regarding the 2012 Games but none of it seems defined at the moment," said a British security official, speaking on condition of anonymity because of the sensitivity of his work. "This is to be expected though with an event of this magnitude."

About 12,000 police officers will be on duty each day of the July 27-August 12 games, which have a security budget of 475 million pounds ($770 million).

British officials say the country has the experience and know-how in dealing with terrorism.

"I am as sure as you can possibly be one year out from a games that we have done everything that we need to deliver a safe and secure games," Olympics Minister Hugh Robertson said.

Extra surveillance cameras will also be installed around the park - Britain has some of the most extensive surveillance powers in the world and has become a leader in what critics call "Big Brother" techniques with its more than 4.3 million closed-circuit cameras in operation.

All Olympics workers will be put through a vigorous screening, including checks for terror and other criminal offenses.

Organizers are determined to keep security from being overwhelming. They point to the successful policing of the royal wedding in April of Prince William and Kate Middleton, when a million people lined the procession route from Westminster Abbey to Buckingham Palace.

"We're very good at policing in a friendly and a discrete way," organizing committee leader Sebastian Coe said. "The real challenge is to maintain security to protect the athletes, protect people, protect assets, but at the same time having people leaving your city feeling they haven't been pushed from pillar to post."

Despite the tight security, London wants these games to be a party.

London promises knowledgeable fans, packed venues, "live sites" with giant screens around the city and a "home" crowd of citizens from different nationalities, cultures and backgrounds. It will all kick off with an opening ceremony created by "Slumdog Millionaire" director Danny Boyle.

"Wait till you see that opening ceremony. I think you will be weeping tears of joy after that opening ceremony. That's my confident prediction," Johnson said.

London has enjoyed a comparatively smooth and crisis-free ride so far. On the down side, the British public has complained bitterly about the ticket sales process, and London's strained public transport system faces tough challenges to keep the city moving smoothly during the games.

On Wednesday, London will mark the year-to-go milestone with a televised ceremony from Trafalgar Square, with International Olympic Committee President Jacques Rogge on hand to formally invite the world's athletes to the games. Organizers will present the design of the Olympic medals and, in the Olympic Park, British medal hopeful Tom Daley will perform the first dive into the Olympic pool.

"If we compare with previous games, we are well advanced and this is a very comfortable position,"said Denis Oswald, the Swiss IOC executive board member who leads the coordination commission for London. "This is especially the case when you don't have to worry about construction and you can really concentrate on the operations side."

Olympic organizers say 88 percent of the venues and infrastructure work for the games has been completed. The Olympic Park in Stratford has a set of gleaming new venues, including the main Olympic Stadium, the velodrome, handball arena and temporary basketball arena. The aquatics center, with its sweeping wave-shaped roof, will be formally completed on Wednesday.

Over the next 12 months, organizers will install the track in the stadium, dress up the venues, finish the landscaping and complete the Olympic village on the edge of the park.

The 226-hectare (560-acre) site is the centerpiece of a massive regeneration project that is turning a former industrial wasteland into a huge urban park. Bordered by a giant new shopping center and new transport links, the park is designed to serve as a vibrant new neighborhood after the games.

The future of the 486 million pound ($787 million) stadium, however, remains in dispute. The Olympic Park Legacy Company selected West Ham football club to take over the arena after the games. But rival London club Tottenham, which proposed taking down the stadium and building a new one without the running track, is challenging the decision in court.