The demolition of the Brighton Centre will be delayed for 12 months while a substitute venue is built.
Plans to bulldoze the seafront conference centre and concert hall at the end of 2005 have been put on hold.
It will remain open until the completion of a 10,000-seat ice palace and arena at Black Rock, expected in summer 2007.
This will become the city's main conference venue until a replacement Brighton Centre is built.
The delay follows a meeting of the all-party project board which will supervise the building of a replacement centre on the same spot.
Property councillor Simon Burgess said: "There has been a lot of work behind the scenes to ensure the city gets the most from this once-in-a-lifetime opportunity.
"There are some very exciting possibilities. It's essential to explore absolutely every avenue in order to get the best possible redevelopment package for the city.
"We are committed to creating a landmark building which is a major driving force behind the city's economy."
Deputy council leader Sue John said the authority wanted to end uncertainty about 2006 bookings but the centre, which opened in 1977, was reaching the end of its lifespan.
Lib Dem group leader Paul Elgood said: "There is cross-party support for this action."
A spokesman for Brighton and Hove City Council said the authority had been sounding out conference organisers, including those in the international market.
They want a high-quality building but most say they would need a maximum of 2,500 seats, half the capacity of the present building.
The building must also have plenty of break-out space and room to house associated exhibitions.
It is possible the new centre could sometimes be used just for exhibitions.
The council spokesman said a development brief would be released in the summer inviting interest from contractors.
The centre's big advantage is its seafront location, a train ride from London, close to the shops and the main hotels. But it has been left behind as other cities jump on the conference bandwagon with more modern buildings.
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