Fences have been erected in a number of Paris streets and a bridge has been put up around the cathedral as specialists prepare to start work.
The culture ministry said workers planned to use two decontamination techniques including spreading a gel on public benches, street lights and other fixtures to absorb the lead.
It will then be allowed to dry for several days before it is removed.
High pressure water jets with chemical agents are also to be deployed in the clean-up operation.
Work inside Notre-Dame that was suspended last month for safety reasons will resume next week.
Hundreds of tonnes of lead in Notre Dame's spire and roof melted during the fire.
Last week, health officials said a child in the city was at risk of lead poisoning after hundreds of children were tested following the fire.
The youngster needs monitoring following tests but does not yet need treatment.
Checks are being done to find out whether the lead came from the fire at the famous 12th century landmark or another source.
The child's school, near the cathedral, was closed in July after high lead levels were found on its grounds.
Despite the move, authorities' response has been criticised, and in July a French environmental group sued Paris officials.
The spire and roof were devastated but the cathedral was saved from total destruction.
An estimated 12 million people flock to Notre-Dame each year, making it one of the world's most popular tourist attractions.