Garda Commissioner Martin Callinan is seeking money to cover the massive security costs of the official state visits by Britain's Queen Elizabeth and US President Barack Obama.
Commissioner Callinan revealed he asked the cash-strapped government for funding after claims "Armageddon" would strike the trips unless the shortfall was plugged.
"It would be unreasonable in my view to expect that the Garda budget would sustain the type of pressure required to put a security operation of the magnitude we are about to put in place," he said.
A rank-and-file police leader predicted 25 million euro was needed to bankroll the double security operation next month.
PJ Stone, general secretary of the Garda Representative Association (GRA), said policing budgets will not cover the planning, surveillance and intelligence gathering needed.
Asked what would happen if the money could not be found, Mr Stone - who represents frontline police officers - said: "Then we are looking at Armageddon."
Mr Stone said: "I don't think the Garda Siochana will be in a position to police those events given the resources that currently exist if there is not a separate budget for this venture."
The garda grassroots leader said when the force was allocated 1.4 billion euro for its budget this year, nobody foresaw the expensive official state visits.
The Queen is to tour a number of historically significant sites during her trip, from May 17 to 20, including Croke Park - the scene of a massacre by British troops - and Dublin's Garden of Remembrance, which honours all those who fought for Irish freedom.
It will be the first official visit by a British sovereign to the Republic. President Obama is expected in the following days.