Lord Coe has said the International Olympic Committee's (IOC) visit to London signals the start of a journey to present "the best Games ever".
Lord Coe said the Games would leave a "permanent legacy"
The organising committee chairman was speaking at the start of a two-day visit by the Co-ordination Commission.
Lord Coe said he was delighted to begin preparations for 2012 which he said would leave a "permanent legacy".
The IOC's team received the first progress reports from organisers and visit venues in east London.
"Our vision is to present to the world, in 2012, the best Games ever, for athletes, for the Olympic family, for spectators," said Lord Coe.
Best Games ever
"This is not just simply about six weeks of successful Olympic or Paralympic sport.
"The IOC comes to town not as a police force, they come to town as partners.....to help and support and monitor and advise and give guidance."
Organisers have six years to transform Stratford into a 500-acre Olympic site.
Lord Coe confirmed the new stadium could become the home for a Premiership football club after 2012, but also said a modern international athletics stadium would be an integral part of the Games legacy.
There have been doubts about whether the project can be delivered on time, particularly in light of the problems that have dogged the £757m Wembley Stadium.
But the IOC stressed that its team was in London to help the city's attempts rather than find fault.
Spokeswoman Giselle Davies said: "The Co-ordination Commission does not want to be seen as watchdogs.
"There is a monitoring role but there has been a big shift of emphasis towards helping and advising and using the expertise within the IOC to help the organising committee."
Review of costs
Culture, Media and Sport Secretary Tessa Jowell said that the cost of staging the Games would be kept in check.
She said: "We are carrying out a review of all the costs and that will be a continuing discipline.
"We expect some costs to rise, but others will come down. We are right on top of that process."
London mayor Ken Livingstone insisted the games would be good for the capital's business.
There are currently some 400 complaints from about 100 objectors, and he said many of these may be withdrawn before a land purchase inquiry begins in May. About 90% of employers have reached an agreement.
The co-ordination commission visit edsites including:
- The O2 Centre (formerly known as the Millennium Dome) which will host the Olympic gymnastics and basketball events.
- The site in Stratford, where four tunnelling machines began work this month to route power cables underground. This could take until 2008 to complete.
- The Holden Point observation platform overlooking the Olympic Park site in east London's Lower Lea Valley. Inflated colour blimps will be used to identify the locations where work is underway
- The Channel Tunnel Rail Link (CTRL) at the new Stratford International Station. This will provide infrastructure for the Olympic Javelin rapid rail shuttle that will transport spectators from central London to the Olympic Park in just 7 minutes.
The commission is led by 58-year-old Swiss lawyer Denis Oswald, an Olympic rowing bronze medallist in 1968.
It also includes Namibia's former world 200m champion Frankie Fredericks and Morocco's 1984 Olympic 400m hurdles champion Nawal El Moutawakel.