TRENTON, N.J. -- Bucking party leaders who urged him not to run, U.S. Rep. Rob Andrews has decided to challenge Frank Lautenberg for the Democratic nomination for U.S. Senate.

Andrews told Democratic officials of his intentions Wednesday, 48 hours after his conspicuous absence from Lautenberg's formal re-election announcement in Trenton.

"I have decided that I will place my name and my credentials before the people of New Jersey to serve as their new United States senator," Andrews said. "The people of New Jersey deserve to choose their senator."

State and national party leaders tried feverishly over the past 48 hours to dissuade the eight-term congressman from challenging the 84-year-old Lautenberg.

Democrats hoped to avoid a primary because it could be divisive for the party and costly for the candidates. But Andrews said he would not be intimidated because some influential Democrats don't approve.

"This is a David vs. Goliath situation," Andrews said in a telephone interview. "All the Goliaths don't want this David to run, but he's going to. I think the public's looking for some Davids to step up and run against the Goliaths."

Andrews, 50, has been South Jersey's 1st Congressional District representative since 1990. Lautenberg seeks another six-year term, which would expire when he turns 90.

Andrews promised to focus his campaign on the Iraq war, which he originally voted to support, the economy and bringing "people of all backgrounds together in the great common cause of making our country better."

Andrews is a clear underdog to Lautenberg. The incumbent senator has amassed $4.3 million for the campaign, is known to most voters and lined up the support from many of the state's most influential Democrats, including Gov. Jon S. Corzine.

Andrews must relinquish his House seat to run for Senate. He has $2.4 million on hand for that race, Federal Election Commission records show.

Lautenberg, currently the third-oldest member of the U.S. Senate, and Andrews will square off in a June primary. Morristown Mayor Donald Cresitello also has indicated he also intends to challenge Lautenberg.

Three Republicans are also seeking the seat.