A strange thing happened to Tom Kean Jr.'s smooth path to the Republican Senate nomination: The GOP came up with a conservative challenger after backing Kean's candidacy.

That's life in New Jersey politics.

The moderate Kean, son of the popular former governor, is still expected to capture the party nod in the June 6 primary, but the Republican challenge from John Ginty, a financial data analyst and political neophyte, has complicated his bid.

Kean, who should be solely focused on a tough fight to unseat Democratic Sen. Bob Menendez this November, must first answer to conservatives for his support for some abortion rights, the state's strict gun control laws and embryonic stem-cell research.

"The voters will have to decide if Tom Kean Jr. is too liberal for Republican primary voters," Ginty said. "There's not much evidence to date that the Kean campaign is interested in conservative solutions to this country's problems."

Kean is confident he can unite conservatives behind his candidacy.

"I have spent my career trying to pull people together to try and find real, common sense solutions to problems," said Kean, a freshman state senator who cited the support of many of the state's leading conservatives, including former Jersey City mayor Bret Schundler.

Conservatives make up 30 percent to 35 percent of New Jersey's 893,854 registered Republicans, according to GOP and conservative officials.

In 2001, strong turnout from New Jersey conservatives lifted Schundler to a win over the more moderate Bob Franks in the Republican gubernatorial primary. In the general election, however, Democrat James McGreevey defeated Schundler.

"They have a very intense interest in politics and passion is a very, very important ingredient in turnout," Ross K. Baker, a political scientist at Rutgers University, said of conservatives.

But in this Democrat-leaning state, New Jersey traditionally favors centrist-to-liberal candidates. Recent polls show Kean and Menendez running about even, with voters typically making their choice in the campaign's final days.

Kean figured the road to the nomination was clear when he secured an endorsement last month at the Bergen County Republican Convention. Bergen, a wealthy, bedroom community for New York city workers, has the most registered voters in the state with more than 506,000 out of 4.83 million.

Divisions within the party were on display, however, when conservative county chairman Guy Talarico ended the meeting, angering moderates who said they hadn't been given a chance to speak. The session concluded with shoving, shouting and obscenities.

Within days of the meeting, the Bergen County GOP delivered an ultimatum to Kean: Endorse our slate of candidates in writing or else we'll withdraw our endorsement. If Kean didn't respond in three days, they would push a conservative to replace him.

Kean ignored the threat, saying: "I don't respond to ultimatums."

The hard feelings lingered and conservatives drafted Ginty to challenge Kean.

"We believe John Ginty has the correct message and the charisma to pull that same kind of grassroots support," said Michael Illions, director of GOPUSA Northeast, a group designed to spread the conservative message. "We helped him collect the petitions that got him on the ballot to begin with."

Baker argued that Ginty will get no farther. Kean is popular enough among all Republicans to defeat the conservative and the party sees Kean as its best chance after a three-decade drought. New Jersey has not elected a Republican to the Senate since 1972.

Kean's spokeswoman, Jill Hazelbaker, said Ginty has every right to run but the campaign remains confident their Republican base will remain strong through November.

Ginty, 41, is busy trying to raise money while Kean, 37, has $2 million cash on hand.

While Ginty is confident he can pull an upset, voters appear to be lining up in Kean's corner, thanks in part to Democratic Gov. Jon Corzine's unpopular budget proposals, which include several tax increases. Corzine appointed Menendez in January to serve out the remaining year of his Senate term.

Enzo Olivieri, the owner of a small auto body shop in nearby Bloomfield, N.J., said it's getting harder to stay in business in the state.

"Everybody's tired of the same old stuff, we need change," Olivieri said.