Growing up in the South Bronx, Ken Lipper sat at his grandmother's knee, tallying the hems and collars she sewed. The 7-year-old boy wanted to ensure the immigrant from Russia, who spoke no English, was properly paid.

Now Mr. Lipper says he's protecting the public purse. At 72, he's prosecuting an idea from his tenure three decades ago as a deputy mayor under Ed Koch to help steer the Port Authority of New York and New Jersey away from real-estate ventures such as the World Trade Center and back to its core mission of maintaining bridges, tunnels and the region's primary airports.Mr. Lipper is fighting a plan to provide a $1.2 billion loan guarantee to 3 World Trade Center developer Larry Silverstein, a stance that's pitted him against fellow commissioner Scott Rechler, also an appointee of New York Governor Andrew Cuomo. The debate at an agency better known for its secrecy follows the departures of senior officials in a political scandal over deliberate lane closings last year at the George Washington Bridge."I don't have any mortgages, I'm free and clear," Mr. Lipper said Thuirsday in a telephone interview. "I'm insulated from threat. I'm free to do the public's business without ambition."Mr. Lipper arrived at the Port Authority last year, capping a five-decade career in which he made millions as a Wall Street banker, weathered investors' lawsuits over fraud at a money management firm he founded, waged an unsuccessful bid to serve as City Council president and served as an adviser for Oliver Stone's Wall Street.