His efforts were undercut in Parliament, where the chief executive of the G4S security group, Nick Buckles, acknowledged that his company's failure to recruit enough Olympic staff had embarrassed the entire nation. Some 3,500 British troops including some just back from Afghanistan had to be called in on short notice to fill the gap. Thousands more military personnel had already been assigned to the games.
Buckles gave a groveling mea culpa on live TV as he was being questioned by angry lawmakers.
"It's a humiliating shambles for the country, isn't it?" asked Labour lawmaker David Winnick.
"I cannot disagree with you," Buckles said.
He was hard-pressed to explain why his company had failed to tell officials until only two weeks before the start of the games that its recruitment efforts had failed.
Some U.S. security and law enforcement officials had privately expressed concerns as early as last year that there might not be enough personnel for the London Games.
The FBI is sending about two dozen agents to London to work on Olympic security, according to two U.S. government officials. They spoke on condition of anonymity because they were not authorized to talk publicly about the plans.
G4S will pay for its mistake, saying it expects to lose between 35 million pounds and 50 million pounds ($54 million to $78 million) on the contract, which is about 12 percent of its annual profit.
Olympics minister Hugh Robertson said the deployment of soldiers at Olympic Park would give people "enormous reassurance."
Robertson, an army veteran, said athletes are "incredibly reassured to see the armed forces on the gate."
About 2,500 of the additional personnel will be housed in East London at Tobacco Dock, a 19th century tobacco warehouse now used as an exhibition center, the military said.
Outside Parliament, hundreds of London cabbies ignited new traffic jams as they protested their exclusion from special Olympic lanes set up across the city's roads for buses and cars carrying athletes and other VIPs.
As the world's athletes flew into London on Monday the first big day of Olympic arrivals a few buses carrying them from Heathrow Airport took a wrong turn and got lost.
"OOPS!" headlined The Sun tabloid, using two of the interlocked Olympic rings in the word.
"First day. First arrivals. It's going to happen," said Jayne Pearce, head of press operations.
Still, the lost buses one carrying Americans, the other Australians touched a nerve. From the very start, London organizers have feared repeating the transportation woes of the 1996 Atlanta Olympics, where one of the biggest problems was hiring bus drivers from outside the city who didn't know their way around.
Coe urged optimism, despite a Twitter storm that erupted when U.S. hurdler Kerron Clement took to the social networking site to express frustration with what he said was a four-hour bus ride from Heathrow to the athletes village.
Coe said Clement's bus journey actually took 2 1/2 hours and most athletes experienced no problems in reaching the village.
"Apart from a misturning and a couple of tweets, we're in pretty good shape," Coe quipped. "The majority of athletes got in in good shape and on time. When they were met by our village mayor and chief executive, they were busily tweeting, saying how much they were enjoying village life. Ninety-eight percent of these journeys went without a hitch."
At Heathrow itself, the airport sailed through its heaviest passenger day ever with short immigration lines and plenty of help for Olympic travelers.
Coe also played down complaints about a miles-long traffic jam caused by the opening of the Olympic lane on the M4 highway from the airport into the city.
"I understand there was an accident at Reading, which slowed some stuff down, but the vast majority of people got through and it seems to be working quite well," he said.
The Olympic "Games Lanes" remain a contentious issue. Hundreds of London cab drivers blockaded the square outside Parliament on Tuesday, blaring horns and snarling traffic to protest their exclusion from the lanes. The cabbies claim it will be all but impossible to ferry passengers around once most of the special lanes take effect July 25.
Britain's notorious rainy weather may prove an even more intractable problem.
Coe said "we've got mops and buckets" to deal with the incessant rain that has soaked London for most of the summer. There is waterlogged ground at two key venues rowing at Eton Dorney west of London and equestrian at Greenwich Park, south of the Thames River.
"It is a problem," Coe said. "It is causing us extra challenges now."
Organizers are resurfacing areas at the two venues, laying down temporary tracking for vehicles and spectators, and putting up special tent shelters to keep the workforce dry, he said.
Although forecasters say the weather could clear in time for the July 27 start of the games, Coe noted that organizers have contingency plans. Extra competition days were built into the schedule "as a last resort" for rowing and equestrian. There is an alternate course available for sailing events at Weymouth, in southeast England, and Wimbledon has a retractable roof over Centre Court for tennis.
Olympic Park, however, still resembles a construction site, with workers laying cables, installing seats and landscaping grounds Tuesday.
Not to worry, Coe said.
"Our venues will be open on time," he promised. "There is still stuff to be done, but it's about dressing up. We'll be ready."
Organizers also said they are reducing capacity at several stadiums hosting soccer matches after failing to sell all the tickets.
More than 1 million soccer tickets had been left unsold recently, but organizers cut the number by reducing capacity by 500,000 at the various venues, which means they might not open a section or a top tier of the stadiums.
Organizers said 250,000 soccer tickets are still on sale and that an additional 200,000 tickets will go on sale soon after being returned by national Olympic committees. A further 150,000 free tickets could be released for schoolchildren.