Will Mitt Romney have enough money for the battles ahead?

The Republican presidential candidate is scrambling to shore up his coffers for a grueling run of primaries over the next month, contests that could go a long way toward deciding the outcome of a nomination fight that has become much tougher, and more expensive, than anticipated.

The former Massachusetts governor and private equity manager has amassed far more money than his competitors and has a deep-pocketed super PAC spending unlimited funds on his behalf. Aides and fundraisers say he will have plenty of money remaining to dominate the contest going forward.

But unexpected surges by Newt Gingrich and Rick Santorum in the early GOP nominating matchups forced Romney to deplete much, if not all, of the money he had on hand at the end of December, increasing the pressure on his campaign to raise millions more as he attempts to secure the Republican nomination.

The money chase illustrates the extent to which Romney has been hobbled by a drawn-out and negative primary contest. His polling numbers among independents have fallen, prompting him to spend resources he would have preferred to use against President Obama in a general election.

In his native state of Michigan, which earlier was considered a virtual lock for Romney, the campaign bought $1.2 million worth of airtime this week to fend off Santorum, who is matching or leading Romney in polling ahead of the Feb. 28 primary there, according to a Republican media buyer. Restore Our Future, the main pro-Romney super PAC, has bought an additional $700,000 worth of ads in the state and is almost certain to spend even more over the next two weeks.

To help pay for the onslaught, Romney has been hopscotching the country holding fundraisers, including a telethon-style gathering at a Manhattan law firm Wednesday in which top bundlers hit the phones to raise money. Romney has also held fundraisers over the past week in Arizona, California and Washington, where he brought in about $1.5 million from a “policy roundtable” with industry lobbyists, corporate executives and other business leaders.

Romney aides and supporters acknowledge the need to raise more money for primaries in Michigan and Arizona, as well as 10 pivotal contests March 6, known as “Super Tuesday.” But supporters say that Romney’s cash flow is fine and that he is locking up more donations from Republicans who had been sitting out the primary race until now.

“We have always said that we’re built for the long haul,” campaign spokeswoman Andrea Saul said. “Gov. Romney will win the nomination because we have the resources, the organization and, most importantly, the message that resonates with voters across the country.”

Romney can dip into a personal fortune estimated at up to $250 million, if necessary, and his supporters note that none of his opponents has the resources of his campaign. Santorum, for example, is spending just $42,000 on ads in Michigan this week.

“Every time there’s a new shiny object out there that’s seen as a potential threat to Mitt, the fundraising picks up,” said David Beightol, a Romney fundraiser and lobbyist at Dutko Grayling in Washington. “The event we did last week was one of our best ever. The energy level, the number of people — everything is going very well.”

Romney, who raised $57 million last year, had about $19 million on hand at the end of December. But he has since spent an estimated $12 million on advertising during the early contests in Iowa, New Hampshire, South Carolina and Florida, and millions more for the travel and other overhead costs of an expanding presidential campaign.

In Florida, his campaign began buying ads a month ahead of the Jan. 31 primary, which he won handily, and eventually doled out more than $6 million.

But the campaign has been more frugal lately, spending almost nothing on broadcast ads last week, according to data from Kantar Media/CMAG, which tracks ad spending.

Overhead expenses also are growing rapidly as the campaign opens offices and hires staff members in numerous states.

Stuart Roy, a spokesman for the Red, White and Blue Fund, a super PAC supporting Santorum, said he was surprised at how little the Romney campaign has devoted to ads over the past couple of weeks given his losses and decline in the polls.

“It’s not that they don’t have money in the bank,” Roy said. “But it probably signals that the money coming in has slowed down, and they want to have the cash to do what they need to do on Super Tuesday.”

One challenge facing Romney is a heavy reliance on the wealthiest donors, who are limited in how much they can assist the campaign. One analysis released last week showed that two-thirds of the money raised by Romney in 2011 came from donors who gave the maximum $2,500.

But many of those donors also have helped by giving to Restore Our Future, which has spent more money on ads than his campaign, data show.

Austin Barbour, a member of Romney’s national finance committee, said this week that it is vital for Romney to keep raising money.

“When you’re trying to become the president of the United States and you’re trying to win a hard-fought Republican primary, it takes a lot of money to win that,” Barbour said. “That’s a competitive advantage for this campaign — we’ve got thousands of donors from all across the country supporting Governor Romney, and our opponents can’t say that.”

Staff writers Amy Gardner in Los Angeles and Philip Rucker in Washington contributed to this report.