British signature architect Norman Foster, Pritzker prize winner Frank Gehry and the RIBA gold medallist Rafael Moneo will be approached by Beirut reconstruction agency Solidere to bid for the project.
Each architect has either worked in Beirut or has expressed an interest in the Lebanese capital.
Angus Gavin, head of Solidere's urban development division, said he was expecting up to 600 practices to enter, but added that it was often difficult to excite interest from larger firms because of the perceived problems of the region.
Gavin said: "We are trying to encourage leading practices to enter. Martyrs' Square was the main focus of the fighting in Beirut. It was so damaged only two buildings survived."
The masterplan not only includes the square, but also the Grand Axis corridor that opens Beirut up to the sea. It covers a space measuring 500 × 300 m and will include a cluster of three towers to the north-east of the site. Buildings on Martyrs' Square itself will have height restrictions to preserve its character.
The competition was originally due to be launched tomorrow to mark Martyrs' day, which is the anniversary of the execution of the Lebanese who plotted to overthrow the Ottoman empire early last century.
However, it is now unlikely to go ahead until the end of the month, once the developer has smoothed out the plans for the competition with the International Union of Architects.
Between five and seven practices will be shortlisted in October. The winning team will be selected on Martyrs' Day next year, following a public exhibition.
When the competition is launched, advertisements inviting bids will be placed on Solidere's website.
The square itself dates back to at least the middle ages. It also marked the termination of the green line that separated Christians and Muslims during the civil war.