The landscape and public realm contract will include hard and soft landscape works, tree planting and the construction of the concourse that will link all the venues, entrances and parklands.
The work, due to start in early 2010, will also include lighting, irrigation and drainage and delivering the London 2012 gardens.
Garden designer Sarah Price has already drawn up plans for the 0.8km-long botanical garden.
The botanical garden - between the Aquatics Centre and Olympic Stadium - will be divided into four zones, representing Europe and the Mediterranean, the Americas, Asia and the southern hemisphere.
The southern part of the park will focus on retaining a "festival atmosphere" from the Games, with riverside gardens and markets in legacy, said ODA head of parklands and public realm John Hopkins.
The pre-qualification questionnaire for the work will be downloadable from www.london2012.com/business in the coming weeks.
Bam Nuttall will start delivery of the northern section of parklands this spring and is now procuring specialist subcontractors.
Four contractors have been shortlisted to supply 500,000 wetland plants (HW, 10 April).
Bidding for two landscape contracts covering soil profiling, tree planting, seeding and turfing, drainage, irrigation, kerbs and paths closed last week. Contractors are expected to be appointed this summer.
Suppliers of 2,000 semi-mature trees for the Olympic Park will be appointed in the coming weeks.