Mayor Boris Johnson previously said it would be too expensive to keep the stadium at its maximum capacity of 80,000, instead backing plans for a 25,000-seat venue.

“I'd be very foolish to rule it out now,” Johnson told The Associated Press on Tuesday.

But he spoke before London legislators issued a report highlighting how the stadium could become a “white elephant” due to a lack of regular sports events after 2012. It points out that while the Bird's Nest was the centerpiece of the Beijing Games, it was now largely dependent on tourism as a source of revenue.

With London Olympic organizers unable to find a permanent football club tenant for the stadium after 2012 — due in part to the running track — it is estimated that the 547 million pound (US$907 million) development could cost 10 million pounds (US$16.5 million) annually to maintain.

But with England bidding for the World Cup in 2018 or 2022, Johnson hopes the Stratford site could become one of the 16 venues. Wembley will take center stage.

Likewise, Twickenham is the English home of rugby union, but the Olympic stadium could also stage matches if the IRB selects England as host of the 2015 Rugby World Cup on July 28. The tournament's rights-holder recommended England's bid on Tuesday.

“It's a very difficult technical subject, but anyone with any common sense looking at this wonderful venue we are constructing in Stratford, will say, 'Why not?”' Johnson said as he launched London's campaign to become a key host venue in 2018.

“It adds hugely to the attractions of London. London already boasts fantastic, incomparable sporting facilities. We are already a leading contender to have the 2018 World Cup, and I think the stadium in the Olympic Park is well worth considering as an additional venue.”

Arsenal's Emirates Stadium and Tottenham's planned new venue alongside White Hart Lane are also in contention to stage World Cup matches in London. FIFA's executive committee will decide the hosts of the 2018 and 2022 tournaments in December 2010.

Retaining the Stratford site as an 80,000-seat venue received key backing last week from Margaret Ford, who will head the Olympic legacy board in September. Lawmakers in the London Assembly plan to press the mayor on how much it would cost to keep the stadium at 50,000 capacity, if not 80,000.

“Margaret Ford ... has been absolutely right to look at the possibility of keeping the stadium going beyond 2012, 2013,” Johnson said. “It's certainly something that people with common sense are going to look at.”

But the London Development Agency has said the stadium cannot make money or break even after the Olympics and would be subsidized by the rest of east London's Olympic Park.

After the Olympics, the stadium will house a secondary school for about 500 students, the National Skills Academy for sports and leisure industries and the English Institute of Sport.