With the wide-open battle for the Republican presidential nomination solidifying, Tim Pawlenty moved quickly Monday to offer himself as the leading alternative to presumptive front-runner Mitt Romney and to seize the mantle of a tough, truth-talking fiscal conservative.

In formally announcing his campaign here, Pawlenty sought to command the space that Indiana Gov. Mitch Daniels would have occupied had he decided to run. The former Minnesota governor cast himself as a serious candidate for serious times and presented a bold agenda to substantially scale back the role of government.

Pawlenty said he would downsize or eliminate popular programs, including gradually raising the retirement age for Social Security, overhauling Medicare and phasing out ethanol subsidies — not normally a popular position in this farm-heavy state.

“Some people will be upset by what I’m saying,” he said. “Conventional wisdom says you can’t talk about ethanol in Iowa or Social Security in Florida or financial reform on Wall Street. But someone has to say it. Someone has to finally stand up and level with the American people.”

With Daniels, former Arkansas governor Mike Huckabee and real estate mogul Donald Trump deciding against a run in the past several days, the GOP contest now focuses squarely on Romney and the two former governors vying to be the leading alternative, Pawlenty and Jon Huntsman Jr. of Utah, who recently stepped down as President Obama’s ambassador to China.

Several underdogs could emerge, as well, including former House speaker Newt Gingrich (Ga.) and, if she runs, Rep. Michele Bachmann (Minn.).

Ed Gillespie, a former Republican Party chairman and longtime strategist, said that with Daniels not running there is an opening for candidates to focus on government spending and debt.

“Pawlenty was smart to jump on it today,” said Gillespie, who is not backing any candidate. “I think he’s got legs. He’s someone who can last in this race and I would not be surprised at all if he ended up with the nomination.”

Elsewhere within the GOP establishment, however, there were fresh signs of concern Monday that the lineup does not have a thoroughbred strong enough to win back the White House.

House Majority Leader Eric Cantor (R-Va.) encouraged others to consider jumping in, telling reporters that he wants candidates to “embrace a leadership role that takes the tough positions.” Although he said he thought the current candidates were “strong,” he added, “I think that our field is a field that still has, you know, a lot of time.”

The absence of Daniels and other identifiable fiscal conservatives, including New Jersey Gov. Chris Christie, presents an opportunity for Pawlenty, who remains a relative unknown despite two years of reaching out to party members and leaders.

“Pawlenty should be bouncing off the walls right now,” said Fred V. Malek, a longtime GOP fundraiser and strategist who is neutral in the race. “It positions him much more securely in Iowa and I think he is, of all of them, the more natural inheritor of the support that was going to Daniels.”

Pawlenty and his advisers have been working behind the scenes to secure support from those who would have backed Daniels. “I think that Mitch and Pawlenty both sort of competed in the same space — certainly geographically and ideologically and probably temperamentally,” said former congressman Vin Weber (Minn.), a top Pawlenty supporter and adviser.

But of the major candidates, Pawlenty has one of the lowest national profiles and has lingered in the single digits in most public polls. And he has struggled to find a firm identity in the race, at times trying to appeal to grassroots tea party activists — at one point supporters started calling him Tea-Paw instead of T-Paw, his standard nickname — and at other times reaching out to establishment figures.

For Pawlenty, winning or outperforming expectations in the Iowa caucus is critical to his campaign strategy. Pawlenty, 50, is an evangelical Christian and has visited Iowa 14 times since November 2008, more than any other potential candidate, according to Iowapolitics.com. And he has hired longtime Iowa operatives.

In beginning his campaign here, Pawlenty presented himself as uniquely positioned to unite the tea party, evangelical and establishment wings of the Republican Party.

In a 20-minute speech before a few hundred supporters on the terrace of the Iowa Historical Building, he did not mention any of his GOP rivals. Instead, he trained his fire on Obama.

“Fluffy promises of ‘hope’ and ‘change’ don’t buy our groceries, make our mortgage payments, put gas in our cars or pay for our children’s clothes,” Pawlenty said.

He added, “Politicians are often afraid that if they’re too honest, they might lose an election. I’m afraid that in 2012, if we’re not honest enough, we may lose our country.”

In a video released on the eve of his announcement speech, Pawlenty contrasted his simple style with Obama’s “fancy speeches” and campaign flourishes, showing footage of teleprompters to make the point. Yet in delivering his speech here, Pawlenty read from a teleprompter, one of the few times he has done so.

In his speech, he made a veiled reference to Romney as he assailed Obama’s health-care plan. Some Republicans have criticized Romney for signing into law a similar plan for Massachusetts.

“I know how to do health-care reform right,” Pawlenty said. “I’ve done it at the state level. No mandates, no takeovers, and it’s the opposite of ‘Obamacare.’ ”

On Friday, Romney will make his first appearance this year in Iowa, although his campaign has shown few signs of competing aggressively in the caucuses here, instead focusing on New Hampshire, the next stop on the 2012 calendar.

Earlier this month, Romney announced that he had raised more than $10 million in one day, a feat few candidates, including Pawlenty, are likely to match. On NBC’s “Today” show on Monday, Pawlenty was asked whether he could raise enough money to be competitive.

“We’re not going to be the money champion in the race,” he said. “It may not be the BMW or the Mercedes campaign, but it’s going to be a good strong Buick, and maybe trending toward a Cadillac.”

Staff writer Paul Kane in Washington contributed to this report.