NEWARK, N.J. — A week after a South Jersey Democrat decided to challenge a North Jersey incumbent for the Democratic U.S. Senate nomination, an old battle is brewing anew: the division in New Jersey between North and South.

In what some worry will blow up into a political civil war over Rep. Rob Andrews’s primary challenge to Senator Lautenberg, pledges of allegiance rooted in geography already have been made.

Mr. Lautenberg, the 84-year-old incumbent who grew up in Paterson, has the support of much of the party’s North Jersey political establishment, from the Senate president, Richard Codey, and the Democratic Party chairman, Joe Cryan, to Mayor Booker of Newark.

Meanwhile, Mr. Andrews, a 50-year-old Camden-born congressman, has been endorsed by much of South Jersey’s political contingent.

“This race is divisive because it brings out the factionalism that already exists within the Democratic Party,” a political science professor at Fairleigh Dickinson University, Peter Woolley, said. North and South Jersey have long seemed divided. Northern New Jerseyans affiliate with New York while those to the south feel kinship with Philadelphia.

A March Monmouth University/Gannett New Jersey poll on New Jersey’s entrenched split personality showed the division means little to residents living in northern areas of the state, but annoys those from the south, who believe their northern neighbors get more government spending. The division extends to politics, where South Jersey has sometimes complained of being big-footed by the more populous North.

Mr. Lautenberg, meanwhile, has heavy support from up North. And, he can count party heavyweights like Governor Corzine, Senator Menendez, and the six Democratic members of the New Jersey congressional delegation in his corner. Also in the race for the Democrats is Morristown Mayor Donald Cresitello. The primary is June 3.