BRENTWOOD, N.H. – Rick Santorum is counting on momentum — and perhaps help from outside groups — to carry him to victory in New Hampshire and beyond. He has little choice.

The little-known Republican presidential candidate doesn’t have much of a staff in most states. He doesn’t have the kind of money his competitors have. And he doesn’t have much time to fix those deficiencies.

New Hampshire’s primary is six days away, and the race quickly turns to South Carolina, Florida and other states where candidates historically need big organizations and big bank accounts to prevail.

“My name is Rick Santorum, and I am the only authentic, passionate conservative who can unite the GOP,” Santorum wrote in a fundraising missive sent as Iowa caucus votes were being tallied in a race he barely lost. “I need an URGENT contribution of at least $35 today to unite conservative voters and win the Republican nomination.”

There were indications the plea may have worked: Santorum has already seen a surge in online donations, which crippled his campaign’s website shortly after the Iowa results were announced. And campaign manager Mike Biundo has said the campaign’s fundraising pace has tripled over the last week.

Even so, Santorum, who nearly won the caucuses after devoting virtually all his time and resources to Iowa, has significant hurdles to climb if he hopes to challenge chief rival Mitt Romney for the party nod.

The former Pennsylvania senator has struggled in recent months to afford campaign basics, such as airfare and rental cars. He’s been largely ignored in the debates. And his lengthy record in the Senate, which includes controversial statements about gay rights, among other social issues, has yet to be fully scrutinized, meaning attacks are likely.

“Santorum still has a lot to prove,” said cultural conservative Kevin Smith, a candidate for New Hampshire governor who recalled presidential campaigns past when “one candidate does very well in Iowa and then fizzles after that.”

Santorum is looking to avoid that fate. Mindful of the challenges, campaign aides stayed out of sight most of Wednesday as the candidate and his small team flew to New Hampshire for an evening rally.

Santorum previewed his likely pitch in the email, saying the time has come for divided conservative voters — as well as tea party activists and so-called values voters — to embrace him.

“We can either unite now behind one candidate and have a conservative standard bearer in 2012, or have the GOP establishment choose another moderate Republican who will have a difficult time defeating Barack Obama in November,” Santorum wrote.

It was a clear slap at Romney and an indication that he wouldn’t shirk from assailing his chief opponent as he looks to emerge as the consensus conservative candidate.

Santorum has vowed to compete in New Hampshire — where Romney has a significant advantage in polls — despite clear vulnerabilities, including that he’s barely registered in surveys here this year. The electorate here also is far less conservative on social issues, which is Santorum’s strength.

Perhaps his biggest weakness is that he has virtually no campaign presence on the ground in any other early voting state. In contrast, Romney and Texas Rep. Ron Paul both have organizations in several states.

That takes money — and Santorum hasn’t had it all year. He reported less than $200,000 in his campaign account at the end of the September, the most recent figure publicly available. Romney, by contrast, finished the quarter with $14.7 million.

Campaign manager Biundo said Santorum was trying to add staff. But he also cautioned that giant payrolls don’t guarantee wins.

Romney himself proved that. Four years ago, he had 52 aides in Iowa and still came up short to Mike Huckabee’s shoestring operation. Huckabee, however, faded as the contest moved beyond Iowa.

“We are going to hire more people, but we are not going to spend millions and millions of dollars like these other campaigns. We feel that we can do it a little bit different,” Biundo said.

A so-called super PAC dedicated to helping Santorum could be a key to his success, or lack thereof, going forward. The group, Red, White and Blue, spent money in Iowa in the final weeks of Santorum’s campaign. It can accept unlimited donations and spend freely.