Councillor Murray Cleveland said the lapse was unacceptable and said replacing it "could be as simple as re-adopting the previous by-law".
A replacement by-law has been prepared and while there were no dramatic changes it would still have to go out for public consultation. Submissions close on December 8.
Whanganui Police Senior Sergeant Andrew McDonald told councillors this week that having the by-law in place before Christmas was "very important".
"Liquor bans can mean the difference between someone having a good time or someone becoming either the victim or the violent offender," he said.
Policy advisor Alex Staric said the lack of an operative by-law was highlighted following an alcohol-related incident in Anzac Pde on October 22 when a number of people were involved in a brawl.
"This incident made it evident to police that they lacked sufficient alcohol control powers ... previously provided under the by-law that expired this year," Mr Staric said.
The original by-law was regarded as a preventative tool and gave police powers to arrest, search and fine anyone found drinking, bringing or possessing alcohol in what had been referred to as the liquor ban areas. Without the by-law there's no legal authority that makes it an offence.
The ban covered much of the central business district, areas in Anzac Pde near the City Bridge and the Durie Hill tower. It also takes in Mowhanau domain, Kowhai Park and Victoria Park on set dates and times.
Mr Staric said if council didn't adopt the by-law then it would effectively leave the police powerless to enforce alcohol control in public places which he said posed a risk "and potential elevation of alcohol-related harm across the district" especial in known hot spots.
Council is also expected to adopt its own local alcohol policy (LAP) before the end of the year. This will enable council to place controls on hours, locations and numbers of on, off and club licences in the district. The LAP and the by-law are intended to work in tandem to minimise alcohol-related harm and diminish public nuisance.