LONDON — The stadium is up and ready to go, the final rehearsals all completed. In central London’s main shopping district, rows of giant flags representing 206 countries flutter over Regent Street, reminding even the most focused shopper: The Olympics are here.

London’s cheerleading mayor, Boris Johnson, has long boasted that the British capital is more than ready for “the greatest Olympics ever.”

The trouble is, not everyone shares his characteristic confidence. The two most common worries Londoners raise: Will it rain miserably? And will the subway work?

With less than 40 days left until the July 27 opening ceremony, many Londoners remain ambivalent about the city’s ability to host the grand event.

The tube

The biggest fear is that the Tube — the city’s creaking, unreliable, century-old subway system — will let the Games down.

“It will be a nightmare. It’s busy enough as it is,” said Carl Read, a manager at a security firm. “I don’t think the Tube will be able to cope at all.”

He’s not paranoid. Nor is he alone in being pessimistic. Despite a 6.5 billion pound (US$ 10 billion) investment in lengthy upgrades, London’s Tube system remains notoriously susceptible to bottlenecks, delays and signal failures. Disruptions are still as common as ever; in May, almost 800 passengers were stuck for hours on the Jubilee Line, one of the key lines that connect to the Olympic Park, and had to walk down a tunnel to safety.

Officials can only keep their fingers crossed that everything else will run like clockwork as an estimated 6.5 million visitors descend on the city.

London revamp

Those who know London will find much of its center subtly improved — cleaner, neater, decked out with festive banners. Traffic will likely be lighter, with many told to work from home.

The subway, for all its problems, has newer, more comfortable trains, and free Wi-Fi at some stations. Heathrow Airport, so often a nightmare to get through, has pledged extra staff to handle the crowds.

Newcomers nervous about navigating such a sprawling city can expect a hand from an army of 8,000 brightly-dressed, trilby hat-wearing volunteers — called Team London Ambassadors — who will be stationed at the airport and around town to provide smiles and tourism advice.

Well protected

One of the most noticeable changes is that the city and its public transport system will be crawling with police and security officers.

The venues will be secured by some 23,700 people, including members of the military. That doesn’t include some 12,000 police officers deployed on the busiest days in hopes of averting a security nightmare like last August’s wave of rioting, or even worse: a terror strike. London is mindful of the tragedy of the transit attacks that killed 52 people on July 7, 2005, the day after it was awarded the Olympics.

Airport-style security will be enforced at all Olympic venues. If that leaves any doubt about what authorities are doing to secure the Games, consider the equipment on stand-by: surface-to-air missiles, typhoon fighter jets, helicopters and two warships.

Go east

For the real transformations, look outside the center to east London’s Stratford, the site of the Olympic Park. A poor, long-neglected corner of the capital and a former marsh, the area has had a stunning makeover, with gleaming facilities complete with an athlete’s village, landscaped riverside parkland and Europe’s largest mall right next to it.

While none of the facilities have the grandiose architectural ambition of, say, Beijing’s National Stadium (nicknamed the “Bird’s Nest” for its memorable steel latticework design), visitors will surely be talking about the Orbit, the area’s divisive landmark. You can’t miss it: a bright red, 115 meter (377 foot) twisting steel tower resembling a smashed rollercoaster that juts out of the landscape, it’s a giant sculpture and viewing tower that has been called wacky and visionary in equal measure.

Visitors not going to any of the sporting events can get still buy tickets to enter the Olympic Park and go up the Orbit. But even for that there is only a limited number of tickets, sold in batches on the official website.

The park is connected to the city by more than a dozen transport links, including a high-speed train service called the Javelin Shuttle that takes just 7 minutes from St. Pancras station. Be warned, though: The Javelin is likely to be extremely popular and may attract huge lines, so stay connected and check the official transport updates regularly before taking your journey.

Party spirit

No ticket to any of the sports events? You don’t need one for many of the public parties across the city. Giant screens will broadcast Olympic events live to thousands at Trafalgar Square, Hyde Park and Victoria Park for free, where entertainment will also be provided — including a special appearance by legendary crooner Tom Jones.

Note that 2012 is also a big culture year for London, with a sprawling arts program touted as the most exciting festival Britain has ever seen. Don’t miss the River of Music, a weekend (July 21-22) of free performances celebrating world music across six stages along the Thames.

If you can’t make that, a stroll along the river is one of the best ways to enjoy London at any time. The stretch of tree-lined riverbank south of the river is particularly lovely in the summer. Starting from Waterloo and heading east, a 40-minute walk will let you take in many of London’s most iconic landmarks — the Houses of Parliament, the Big Ben, London Eye, Shakespeare’s Globe and St. Paul’s Cathedral. Look out for a pyramid-shaped skyscraper near Tower Bridge: It’s The Shard, the newest addition to the skyline and Europe’s tallest building.

If the weather doesn’t cooperate, London’s free museums are your best bet for a great morning or afternoon indoors. The British Museum and Natural History Museum are best for the family, the National Gallery and the Tate Modern wonderful for art lovers. All are world class, free of charge, and centrally located.

100 percent occupancy

With so much going on in the capital, it’s no surprise that demand for hotel rooms has far outstripped supply. Most of central London’s hotels are expecting 100 percent occupancy, despite the premium prices. A recent survey by the booking company Hotels.com suggests that the average hotel room rate in central London during the Games is 213 pounds (US$341) — expensive, but not extortionate given the capital’s high costs.

Still trying to fish for a last minute room? One option is to look up short-term apartment or house rentals — more and more landlords all over the capital are putting up their homes on rental websites to take advantage of the tourist inflow.

There should also still be rooms available outside the city center, especially in the farther ends of west London. These may not be as inconvenient as they seem, particularly for visitors with tickets to events held outside the Olympic Park: archery, badminton and tennis, for example, will all take place in west London venues.

Wherever you stay, don’t be disheartened by Londoners’ apparent lack of enthusiasm for the Games.

“It’s the British way,” mused Patrick Smith, a property manager, when asked why so many of his fellow city dwellers are so lukewarm about the Olympics. “We hold back our feelings and don’t like to give anything away.”

And if you’re stuck on the Tube, or caught in the rain — two entirely possible scenarios — just adopt the British wartime poster slogan, that quintessential mantra of British stoicism: Keep Calm and Carry On.