Democratic Sen. Frank Lautenberg of New Jersey, a staunch advocate of gun control and public infrastructure and a champion of the Amtrak railroad system, announced Thursday he will not seek re-election in 2014.

"This is not the end of anything, but rather the beginning of a two-year mission to pass new gun safety laws, protect children from toxic chemicals, and create more opportunities for working families in New Jersey," Lautenberg said in a statement.

Lautenberg, at 89 the oldest senator and the Senate's last veteran of World War II, has been easily elected five times, but he was facing a likely challenge from charismatic Newark Mayor Cory Booker.

He has also had health problems in recent years. He was diagnosed with cancer in 2010 — and successfully treated — and a case of the flu this winter caused him to miss the Senate's Jan. 1 vote on avoiding the so-called fiscal cliff of rising taxes and falling government spending. But he has beaten back health problems before — and a primary opponent who suggested he was too old for the job.

Lautenberg first won election to the Senate in 1982. He was set to travel Friday to his hometown of Paterson to announce his retirement.

In 2008, Rep. Rob Andrews challenged Lautenberg in a Democratic primary, but Andrews fell well short of unseating Lautenberg as most of the state's Democratic Party establishment continued to back him.

Lautenberg was diagnosed in February 2010 with B-cell lymphoma of the stomach and underwent chemotherapy treatments until he was declared in June 2010 to be free of cancer. He worked between the treatments. The diagnosis came just days after the death of Sen. Robert Byrd, D-W.Va., which made Lautenberg the oldest member of the Senate.

Lautenberg got into politics in 1982 after building a fortune as a founder of Automatic Data Processing. In that race, he defeated patrician Republican Rep. Millicent Fenwick, the model for the cartoon character Lacey Davenport in "Doonesbury," while spending $3 million of his own money.

In the Senate, Lautenberg has been a reliably liberal vote, crusading against smoking and youth drinking and supporting gun control and stiffer environmental laws.

"While I may not be seeking re-election, there is plenty of work to do before the end of this term and I'm going to keep fighting as hard as ever for the people of New Jersey in the U.S. Senate," Lautenberg said.

This isn't the first time Lautenberg has retired. He decided not to seek re-election in 2000, a move that opened the seat for Jon Corzine, who later served a term as governor of New Jersey. But Lautenberg was drafted back into politics two years later when scandal-plagued Sen. Robert Torricelli, a Democrat and Lautenberg's longtime rival, abruptly left the race in 2002.