Mayor Rudolph Giuliani wants the mob to give up more than 60 years of control over the bustling, pungent stalls of the nation's largest fish market.

Giuliani announced plans Wednesday to better regulate and investigate businesses and workers at the Fulton Fish Market. He hopes the plans will help clean up what police say has become a dangerous place for those who buck Mafia rules."We have seen the size of the market shrink from approximately $3 billion to $1 billion because there are businesses that will not do business here out of fear," Giuliani said.

Police say the Mafia's Genovese family uses its control over workers and businesses at the market to impose a monopolistic "mob tax" that has driven many fish sellers to do business at other markets on the Eastern Seaboard.

The mob also profits by serving market workers' appetites for gam-bling and loans.

The fish market, on the East River in lower Manhattan, handles 125 million pounds of fresh seafood yearly and employs about 800 people.

It was taken over by Joseph "Socks" Lanza, a fish handler who organized his own labor union in the 1920s. It became a powerful weapon for extortion and, eventually, for control of the entire market.

One of the city's first steps will be to renegotiate leases of the wholesale fish dealers who operate on city property, said Randy Mastro, Giuliani's chief of staff and a former federal prosecutor.

New York City now takes in $268,000 a year in rent from 5 dozen wholesalers, but a federally sponsored study in 1992 put the value of the leases at $3 million.

Under Giuliani's proposal, the market would be managed by the Department of Business Services.