Most London councils failed to reach targets to build affordable homes.
London Mayor Boris Johnson's plan to create 50,000 new affordable housing units by 2011 has been thrown off course by the current economic turmoil.
London Assembly's Planning and Housing committee has heard from experts who called the plan "extremely challenging" at best and impossible at worst.
The committee heard that, for now, the £4bn earmarked for housing should focus mainly on rented social housing.
Experts say the move is best until the property market is more stable.
John Stewart of the Home Builders Federation told the committee that without a sudden rebound in housing prices, new private investment in affordable housing units would not happen.
But Bob Kerslake, of the assembly's Homes and Communities agency, said there might be an opportunity for local councils to work with housing associations and private builders to ensure some units do proceed.
The mayor's Director of Housing, Richard Blakeway, said the mayor remained committed to his target and would work with the agencies involved to come up with answers.
"The difficult market does not lessen London's housing needs," he said. "We are asking the Housing and Communities agency to develop innovative models for delivery in the capital to meet new circumstances."
Committee chair Nicky Gavron said the mayor should urge local authorities to build rental housing, and institutional investors such as pension funds should also be encouraged to invest in new rental housing.