The four-year programme will cover extensive civils and technology works to cut congestion on the bridge and strengthen an associated concrete structure.
The Highways Agency, which is acting on behalf of Connect Plus (M25), is looking at options to let the civils and technology elements separately or bundle the job into one contract.
Civils works at Dartford are planned to include new signalling gantries, demolition of existing toll booths, realignment of carriageways including change from multi-lane to four lane carriageways.
The contract also covers all associated kerbing, drainage, services diversions, lighting, fences and gates and traffic management.
Technology works include installing signs and signalling, vehicle height and width sensors, new traffic signals and road barrier systems, ramp metering and CCTV.
Connect Plus plans to hold a suppliers day on 10 September to detail plans for the Dartford Crossing improvements works.
Interested firms can pre-register by sending company details and names for up to two attendees to email@example.com by 6 September.