The nation’s most competitive Senate primary Tuesday may be 400 miles north of Delaware.

While the national buzz has followed the Tea Party Express to the First State’s GOP battle between Rep. Mike Castle, the establishment pick, and outspoken conservative Christine O’Donnell, the New Hampshire ballot will feature four credible Republican candidates fighting for the chance to replace retiring Sen. Judd Gregg (R).

And while the race dynamics differ in many ways from Delaware, the New Hampshire contest offers a familiar theme: It appears the local tea party favorite, Ovide Lamontagne, is gaining some momentum over the establishment favorite, Kelly Ayotte. An upset could complicate Republican efforts to preserve a Senate seat that’s well within their grasp.

“There’s no way of predicting the outcome,” said Andy Smith, director of the University of New Hampshire Survey Center. “You’ve essentially got a weeklong campaign here. Most people are going to be making up their minds in the last couple days.”

Republican leaders in Washington and the Granite State acknowledge that the path to victory over Rep. Paul Hodes (D) would be easier with Ayotte representing the GOP. She has consistently polled ahead of her Republican opponents and has solid name recognition from her time as state attorney general.

But a recent wave of bad press for possible missteps in her role as the state’s top prosecutor may have hurt Ayotte, as has the high-profile negative battle with wealthy businessman Bill Binnie, who has already poured nearly $6 million of his own money into the race. Lamontagne went up with his first statewide television buy Tuesday — a pleasant 30-second spot that proclaims him “the only true conservative for the U.S. Senate.”

All four Republicans, including another conservative favorite, Jim Bender, are up on television this week, although Binnie and Ayotte have been up for months.

“There’s one campaign with momentum in this race and that’s Ovide’s,” Lamontagne senior adviser Jim Merrill said. “It was a budding surge that’s become a full-throated roar.”

And of course there’s the Sarah Palin-Laura Ingraham “catfight.”

Evidence surfaced Thursday — the day of the contest’s first and only televised debate — on the local blog Now Hampshire that Lamontagne supporter Wendy Long was trying to provoke a fight between the conservative talking heads in a recent op-ed featured in the Manchester Union Leader, which backs Lamontagne.

Former Alaska Gov. Palin endorsed Ayotte weeks ago, while Ingraham has told her national talk-show audience as recently as this week that Lamontagne is the race’s “only true conservative.”

“I tried to inject seeds of a conflict between Laura and Palin as there may be some catfight sparks there that might get attention,” Long wrote in an e-mail to Merrill published by the blog.

At this point, however, there’s no indication that Palin will boost her visibility in New Hampshire, despite signs that the race may be tightening. Democrats hope she will make a surprise appearance.

Ayotte’s “threat through Sept. 14 is going to be from the conservative side,” said Emily Browne, state Democratic Party spokesperson. “It seems like Palin is her top far-right supporter. It’s interesting that she hasn’t brought Palin in yet.”

Democrats want Palin to visit the Granite State for the very reason that she likely won’t come.

Palin is unpopular in New Hampshire and likely has little appeal to the spectrum of voters allowed to vote in the state’s open primary system, according to the UNH pollster Smith.

Palin’s original endorsement didn’t exactly go as planned. It prompted an angry front-page editorial in the Union Leader and left a bad taste in the mouths of some local tea partiers.

“Our take on Sarah Palin is that we don’t consider her to be the leader of the tea party,” one New Hampshire tea party organizer said. “She has made some good picks and some bad ones. A lot of people didn’t like that she picked Ayotte. Palin can’t possibly know New Hampshire.”

But Ayotte’s campaign is unapologetic.

“The other candidates wish they had Sarah Palin’s endorsement. She electrified New Hampshire conservatives in 2008 and she will do the same in this race for Kelly,” Ayotte spokesman Jeff Grappone said.

But do not expect a surge of assistance from national tea party groups in the next five days. Tea Party Express Chairman Amy Kremer confirmed Tuesday that her group would play no role in the New Hampshire race.

“All of our efforts and resources are focused on Delaware. We’re not going to get into any other races before next week,” Kremer said in a phone interview from Delaware, where her organization has gathered about 10 leaders and will host several events and get-out-the-vote efforts for O’Donnell through the primary.

“When we get behind a candidate, we go all in,” Kremer said.

That may be welcome news to Ayotte’s campaign, which offered an optimistic assessment of the race this week despite attacks from the right and the left.

“Kelly Ayotte has led in every poll since before she even started campaigning,” Grappone said. “Kelly has the deepest support of any candidate in the race and has the strongest grass-roots network. She has 3,500 New Hampshire donors and has raised more money in-state than all the other GOP candidates combined. She will win on Tuesday and beat Paul Hodes in November.”