Public Advocate Bill de Blasio — not usually an ally of Mayor Bloomberg — offered a strong and unqualified endorsement yesterday of the administration’s hotly debated plan to establish a new metered taxi fleet exclusively for the boroughs outside Manhattan.

“The five-borough Yellow Taxi and Livery Service Plan is a winner for all New York City residents,” de Blasio (pictured) said in a surprise statement.

“By auctioning new medallions that permit taxis picking up street hails outside of Manhattan, we will improve transportation in the outer boroughs while adding over $1 billion in revenue and thousands of good jobs for New York City.”

The plan calls for the creation of 6,000 “borough only” taxi medallions that would be linked to the auction of 1,500 new regular yellow-cab medallions.

Officials in the livery-car industry are demanding that at least 50 percent of the borough medallions be set aside for their drivers and dispatch bases.