The Olympic Park Legacy Company (OPLC), expected to recommend one of the Premier League clubs on Friday, said it "needed more time" to decide on what has become the most controversial question surrounding the 2012 Games.
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"Given the detailed nature of both bids received, we need more time to seek further clarification with both bidders in order to identify a preferred bidder," a statement from the OPLC, the body responsible for planning the post-Games use of the various venues, said.
"The stadium is a significant public asset and we have a duty to run a robust process.
"Securing the most appropriate solution for the stadium is vital to our long-term aspirations for the future Queen Elizabeth Olympic Park and the wider regeneration of the area."
The future of the stadium, which has cost in excess of 500 million pounds of public funds, has become a sensitive issue because Tottenham plan to knock it down and replace it with a purpose-built football stadium without a running track.
On Sunday, London 2012 organising committee (LOCOG) chairman Sebastian Coe said Britain's reputation would be "trashed" if Tottenham's bid was chosen rather than West Ham's.
"It's serious we deliver what we said we were going to unless we're prepared to trash our reputation," Coe, whose bid team in Singapore in 2005 promised an athletics legacy in the Olympic Park, told the BBC.
"It would be very difficult for us to be taken seriously in the corridors of world sport and arguably beyond."
Coe, together with high-profile members of the International Olympics Committee (IOC) and the athletics governing body the IAAF, favour West Ham's proposals for a 60,000-seater football stadium incorporated in the current structure.
West Ham, who are in partnership with the London borough of Newham, say they will retain the athletics track.
Tottenham maintain that an athletics track inside a football stadium does not work and intend to meet London 2012's legacy promises by revamping the Crystal Palace athletics stadium.
The OPLC also confirmed on Monday that a third option, the original bid plan to strip the stadium down to a 25,000-seat bowl with athletics and community use, is also still possible.
"In going to market, the Legacy Company's aim was to consider options which would enhance and build on that plan," the statement said.
No new date was given by the OPLC but any decision they make would be subject to approval by the Government and the London Mayor Boris Johnson.
