The WWF's annual event aims to reach out to more than one billion people in 1,000 cities around the world, asking individuals, businesses and governments to come together and switch off lights for one hour to promote the fight against climate change.
A pitch process for the account is under way and it is thought that the WWF has now shortlisted a number of agencies.
The winning agency will be responsible for raising the UK profile of the campaign and drumming up publicity around next year's event. Fees for the account are understood to be £15,000.
The WWF often uses pro-bono support from specialist social media agencies such as We Are Social, which works to get online communities to discuss the campaign and draw audiences to the campaign's Facebook page.
Next year's Earth Hour in the UK will take place on 31 March at 8.30pm.