For the first time, New Jersey voters will be asked to elect a lieutenant governor, a role so loosely defined it could be turned into a stepping stone for higher office or a forgotten seat on the back bench.

Democratic Gov. Corzine and Republican gubernatorial candidate Christopher J. Christie say they will pick their running mates at the end of this month, setting off rounds of speculation about who will get the ballot spots.

While Burlington County's Diane Allen, a Republican state senator and former Philadelphia newscaster, has been mentioned, the nominees could come from Bergen County, the key battleground in a statewide race, particularly for Republicans.

The last time a Republican gubernatorial candidate won the county was in 1997, when former Gov. Christie Whitman was reelected, which also was the last time a Republican won a statewide seat.

Bergen County Clerk Kathleen Donovan, a Republican, and State Sen. Loretta Weinberg (D., Bergen), prominently mentioned as lieutenant governor candidates, bring the added advantage of being women on tickets headed by men.

Weinberg has a statewide reputation as a reformer, while Donovan has been able to ring up victories even as Republicans have lost power in Bergen County.

Allen, a Republican, has held her seat in the Democratic-dominated side of Burlington County even as other Republicans have been replaced by Democrats. U.S. Rep. Frank LoBiondo, a Republican who represents the Shore, has also been on the lists of some observers.

Proven vote-getters from Essex, Mercer, Monmouth and Middlesex Counties also have made it to the lists. Neither gubernatorial candidate has publicly named a list of potential lieutenants. Corzine and Christie have 30 days following the June 2 primary to name a running mate.

Two potential candidates - Democratic Newark Mayor Cory Booker and Republican State Sen. Thomas H. Kean Jr. - have publicly said they are not interested in the job.

For Christie and Corzine, the picks will be one of their first moves of the general election, and therefore carefully scrutinized.

"It's going to be a very important decision, particularly for Chris Christie, because it's going to be the first major decision beyond running in the primary that he's going to be making," said Seton Hall University professor of political science Joseph Marbach. "Part of what the selections will show are areas where each candidate feels he needs to shore up his appeal with the electorate."

While candidates are looking for a person who can fill their shoes, they also are "looking for a candidate who can most bring votes to the table," said Sharon Schulman, director of the Hughes Center at Richard Stockton College.

In New Jersey, the lieutenant governor's job will be to serve in the event the governor cannot, which leaves the definition of the role wide open.

Both Christie and Corzine have tried to clarify the role beyond official gubernatorial pulse-taker. Each candidate says he'll pick someone he believes can serve as governor.

Answering reporters' questions last week, Corzine said that beyond that, "we want to make sure this person can operate inside the government, so we can leverage up that person's skill set to hold down costs."

He would probably have his lieutenant in a dual role, adding a cabinet position to his or her responsibilities. Corzine has suggested that he'd go for a woman or a minority "that would give us a greater degree of including everyone in the political process."

Christie said he wants to be compatible with the person, but his lieutenant doesn't have to agree with him on everything. The ideal candidate, he said, would have shown some leadership in government or business.

Christie's lieutenant would head a "red-tape review" committee, to clear out regulations that Christie believes are suffocating business. For the long haul, the lieutenant would head up Christie's job-retention and creation efforts by chairing a consolidated economic development agency.

Lieutenant governors in other states have clearly defined roles in cabinet-level positions. In Ohio, the lieutenant heads the state's economic development efforts, while in Missouri, the lieutenant is in charge of tourism, according to Morgan Mundel, spokesman for the National Lieutenant Governors Association.

New Jersey voters amended the state constitution in 2005 to create the position, following the 2004 resignation of former Gov. James E. McGreevey. His term was finished by State Sen. Richard Codey (D., Essex), who also served as Senate president. In 2001, when Gov. Whitman left to serve in the Bush administration, Senate President Donald DiFrancesco finished her term.

In recent months, lieutenant governors in New York and Illinois have stepped up when the governor left under a cloud of scandal. Since 2000, Mundel said, 17 lieutenant governors have moved into the governor's office.

New Jersey will become the 42d state to have a lieutenant governor, a position that the holders in other states have parlayed into governorships almost 30 percent of the time, Mundel said.

Seton Hall's Marbach said that whether the lieutenant becomes a forgettable figure "will depend on how the office is utilized, and is largely dependent on the leadership style of whomever is elected governor and how he's going to embrace the lieutenant governor."

Contact staff writer Cynthia Burton at 856-779-3858 or cburton@phillynews.com.