LONG before his father was sent to prison forever, John A. (Junior) Gotti showed he was a son a mobster could be proud of.

In 1989, 25-year-old Junior earned $300,000 by using his trucking company to haul illegal loads to a mob-controlled landfill in Matamoras, Pa.

Problem was, the dump belonged to the Lucheses, who complained to Gotti that his son had horned in on their deal. You can almost hear the elder Gotti's chest swelling with pride as Luchese underboss Anthony (Gaspipe) Casso complained about Junior.

"Gotti ... could not believe that his son took $300,000 from the landfill without him knowing it," Casso told the FBI, according to a secret memo obtained by Gang Land.

A $300,000 misunderstanding is serious business however, and it required a sitdown at a Greek diner in Brooklyn, near the construction company office of then-Gambino underboss Salvatore (Sammy Bull) Gravano to resolve it.

At the confab, Junior had a tough time. First he denied it to Casso's face. Then he admitted making a deal with the owner of the landfill. Finally, said Casso, Junior offered him $500,000 for permission to dump construction waste at the fill. He also offered to split dumping fees he charged contractors.

Casso nixed the deal, telling Junior the Lucheses were doing just fine, thanks. The real reason he rejected the partnership, Casso said, was that, like his flamboyant father, Junior was under constant surveillance. If Junior got involved, "hundreds of people would know," Casso said.