Racial tension runs so deep in the Long Island community rocked by an immigrant’s murder last weekend that it’s even scrawled on a sign just 30 yards from the entrance to the high school.

There, the hate-filled word “spic” is crudely scrawled on a stop sign outside Patchogue-Medford HS, where seven teens charged in the brutal, racially charged stabbing death of an Ecuadorian immigrant are students.

Two years ago, school officials had to impose lockdowns after a series of racial brawls erupted between newly immigrated Hispanic students and their white and black classmates. Witnesses say chief slay suspect Jeffrey Conroy was at the center of many of them.

“Jeff was involved in a lot of those fights. I think maybe that got him thinking like this,” said an ex-girlfriend, who asked to remain anonymous. “He had plenty of black and Turkish friends, as well as some Hispanics, but he had a particular problem with illegal immigrants.”

She said she broke things off with Conroy when she noticed he had a small swastika tattoo on his thigh. When she confronted him about it, he said, “It’s what I believe in.”

Conroy and his cohorts hatched the horrific plot to go “beaner jumping” – a derogatory reference to Central Americans – as they drank with others at Southaven County Park on Saturday night, a close friend, Michelle Cassidy, 16, told The Post.

But as most went home, Conroy and his six buddies drove around until they encountered Marcello Lucero, 37, and a friend as they walked down the street. The teens surrounded them, and Conroy allegedly plunged a blade into Lucero’s chest. Cassidy insisted that Conroy had friends of all races, and she couldn’t see how this was a racial slaying.

“It just isn’t,” the teen said outside the school yesterday.

The killing has shaken the area to the core. “There is a lot of racism out here,” said 14-year-old Jonathan Campoverde as he walked past a memorial to Lucero. “People are afraid of walking down the street – little kids now.”

Recently, residents said a pack of menacing teens had been harassing Hispanics walking down Main Street in Patchogue, screaming epithets and telling them to “get the f- – – out of here.”

Back at the school, many said they were hoping the hostility would subside.

“There was a lot of racial tension. It was bad. There were fights in the school. There were a lot of lockdowns, but we took strong measures against it, and it improved,” said one school-board member.

But yesterday, school officials locked the campus down once again, and Suffolk County cops were stationed around the campus. Principal Manuel Sanzone held special assemblies with each class, appealing for unity, students said.

Meanwhile, the Secret Service opened an investigation into racist graffiti spray-painted on more than two dozen vehicles, including messages targeting President-elect Barack Obama in nearby Mastic.

At least one car had “Kill Obama” painted on it.

Suffolk County cops are also investigating reports by several Islip Terrace residents that Ku Klux Klan literature was left on their property Monday.

Additional reporting by Douglas Montero and AP