(Adds Booker comment, background)
WASHINGTON, Feb 14 (Reuters) - Senator Frank Lautenberg, the New Jersey Democrat who at 89 is the U.S. Senate's oldest member, said on Thursday he will not seek re-election to a sixth term next year.
His decision opens a clearer path to the seat for Newark Mayor Cory Booker, the front-runner for the Democratic nomination for Senate in 2014. Booker said he would seek the seat before Lautenberg announced his intentions.
Lautenberg, a self-made multimillionaire businessman who became a leading liberal voice in the Senate, offered no reason for his decision to retire from Congress, but vowed to keep working for constituents until his Senate term ends in January 2015.
"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," he said in a statement.
Booker, 43, is a rising star in the Democratic Party, known as much for his rescue of a woman from her burning home last year as he is for running a city troubled by high crime and unemployment.
Booker announced he would explore running for Lautenberg's seat in December, then filed papers in January, drawing criticism from Lautenberg supporters who suggested the mayor should focus on his own struggling city.
"Senator Lautenberg has been a strong model of leadership and service to me since before I even considered entering elected office," Booker said in a statement after Lautenberg's announcement. "I look forward to continuing to work with him for the remainder of his term in the Senate and for many years to come."
A survey by Public Policy Polling released in November found most New Jersey Democratic voters wanted to see Lautenberg retire at the end of his term in 2014 rather than seek re-election.
The same survey found Booker leading the pack of potential Democratic candidates for the Senate seat, with six in 10 voters saying they want to see him run.
FROM BUSINESS TO POLITICS
Lautenberg was first elected to the Senate in 1982, after incumbent Democrat Harrison Williams quit in a bribery scandal.
Lautenberg had retired from the Senate in 2000, saying he was tired of chasing campaign contributions. But in 2002 he came out of political retirement at age 78, again helping the Democrats retain a seat after Senator Robert Torricelli dropped his re-election bid amid corruption charges involving improper gifts from a businessman.
He was last re-elected in 2008 at age 84.
The World War Two veteran was a co-founder, former chairman and chief executive of the payroll services company Automatic Data Processing.
Booker, a former Rhodes Scholar, burst on the political scene with a failed attempt to unseat entrenched Newark Mayor Sharpe James in 2002. Booker succeeded in ousting James in 2006.
One of the first public figures to understand the significance of social media, Booker uses Twitter incessantly to field questions about potholes, talk about policy and disseminate inspirational quotes.
More than a quarter of Newark's residents still live in poverty. Critics say that as his national profile has soared, he has failed to grapple with problems in his city.
He contemplated a possible gubernatorial run against Republican Governor Chris Christie, a powerhouse with high poll numbers, but opted instead for Lautenberg's seat, forcing the elder statesman's hand.
"This is still a Democratic state and the high likelihood is that this seat gets held by a Democrat," said David Redlawsk, director of the Rutgers-Eagleton Poll.
Lautenberg's office said in February 2010 the senator had been diagnosed with cancer and would undergo chemotherapy. That June Lautenberg said he had recovered completely.
He accomplished a number of things during his tenure in the Senate. He convinced Congress to bar smoking on domestic airline flights and in federal buildings. He has been a strong supporter of gun control and was behind the 1996 law prohibiting people convicted of domestic abuse from owning guns.
He also wrote the law that required U.S. states to set 21 as the drinking age in order to continue to get federal highway aid, a move he says has saved tens of thousands of lives. (Reporting by Thomas Ferraro,; Hilary Russ and Edith Honan; Editing by Daniel Trotta and Stacey Joyce)