The survey by Monmouth University and the Gannett New Jersey asked voters to guess Lautenberg's age.
"The average guess was 75, fully nine years younger than he really is," said Patrick Murray, the poll's director.
Both the Monmouth/Gannett poll and another released Wednesday by the Quinnipiac University Polling Institute showed Lautenberg with a significant lead over his Republican challenger, former Rep. Dick Zimmer. Lautenberg was ahead 48 percent to 39 percent in the Quinnipiac poll and 46 percent to 36 percent in the Monmouth/Gannett poll.
While 59 percent of respondents to the Monmouth/Gannett poll said Lautenberg is not too old to be an effective senator, 54 percent of those in the Quinnipiac survey, who were told he is 84, said he is too old.
But Clay Richards, the Quinnipiac assistant polling director, said Lautenberg's age does not appear to be a major factor.
"Age is a concern but not a deal-breaker in elections," Richards said.