TRENTON - Incumbent Democrat Frank Lautenberg leads his Republican opponent as he seeks reelection to the U.S. Senate, but many voters remain uncommitted, a new poll has found.

The Monmouth University/Gannett New Jersey Poll released yesterday found Lautenberg leading Dick Zimmer by 45 percent to 37 percent among likely voters.

But Patrick Murray, the poll director, said many voters have not committed.

The state has 1.7 million Democratic and 1 million Republican voters, but 2.2 million independent voters.

The poll found 21 percent of independents on the fence and 20 percent of independents saying they might vote for a third-party candidate.

It also found only 64 percent of Republicans willing to support Zimmer less than four months before the Nov. 4 election.

"While Lautenberg leads, many voters cannot commit to either candidate," Murray said. "This is usually bad news for the incumbent. However, Republicans are not showing their typical early support for the GOP nominee. Couple this with the high number of voters entertaining a third-party vote, and it's clear that Dick Zimmer still has work to do with his own base before he can start courting independent voters."

At 84, Lautenberg is the third-oldest senator. He is seeking a fifth six-year term.

Zimmer, 63, is a former House member who ran unsuccessfully for the Senate in 1996.

Thirty-four percent of those polled said they had a favorable opinion of Lautenberg, compared to 27 percent who viewed him unfavorably and 39 percent who had no opinion. Seventy-one percent said they did not know enough about Zimmer to form an opinion.

Thirty-one percent felt Lautenberg is too old, down from 41 percent in April.

But when voters were asked a separate question about age, 46 percent said an 84-year-old is too old to be a senator.

The telephone poll of 874 registered voters was conducted from July 17 to 21 and has a sampling-error margin of 3.5 percentage points.