Rick Santorum has vaulted to the front ranks of the Republican presidential nomination race in part by depicting himself as a religious family man of lowly beginnings who would bring needed change to Washington.

But that characterization leaves out two decades in which Santorum was a central and often high-ranking player in Washington politics, with connections to K Street lobbyists and a lucrative consulting career that made him a millionaire.

In the Senate, for example, he played a pivotal role in advancing the controversial K Street Project, a highly organized effort to pressure industry groups and lobbying firms to hire Republicans for influential jobs and punish those who brought in Democrats. ­Santorum oversaw regular Tuesday meetings with lobbyists in which he solicited their views on pending legislation and discussed potential jobs, according to documents and news reports and a lobbyist who attended the meetings.

After losing a reelection bid in 2006, he capitalized on his congressional experience by beginning a profitable career on K Street as an adviser to industry groups and lobbying firms, disclosure records show.

Santorum’s track record as a longtime Capitol Hill insider is likely to pose a political challenge in the weeks ahead, in part because it undermines his self-portrayal as a reform-minded champion of fiscal conservatism. After spending months languishing in obscurity in the presidential race, he finished just eight votes behind former Massachusetts governor Mitt Romney in Iowa’s caucuses on Tuesday and immediately faced allegations that he had backed wasteful spending and special interests.

Hogan Gidley, Santorum’s national communications director, said Thursday that “these kinds of attacks are just what D.C. insiders and elitists do when a guy like Rick Santorum works hard to provide for his family and has success.”

“From Day One, Rick Santorum fought to destroy the good old boy network in Washington,” Gidley said, pointing to efforts to expose a House banking scandal and urge an end to special congressional perks. “Democrats and some Republicans were furious with Rick, but Rick stood up for the people then, and that’s what he’ll do as president.”

Romney and Texas Gov. Rick Perry, another GOP presidential hopeful, have begun unloading on Santorum in recent days for his role in pushing earmarks and other goodies as part of congressional budget negotiations, a practice that has become sharply limited under House and Senate rules. Some of the earmarks Santorum backed during his 16 years on the Hill benefited local firms or industries, including mining and defense companies whose employees contributed to his political committees, records show.

The Romney campaign highlighted criticism of Santorum on Thursday from Sen. John McCain (Ariz.), the 2008 GOP presidential nominee, who endorsed Romney this week. McCain said on CNN that Santorum championed “earmarking and pork-barrel spending” while in Congress.

“I believe that earmarking is a gateway drug to corruption,” McCain said. “Senator Santorum supported it and engaged in it as much as he possibly could. I strongly disagreed with it.”

Santorum has spent much of his time on the campaign trail focusing on his humble beginnings in Pennsylvania coal country and suggesting that he operates outside the realm of big-money Washington politics. But a review of disclosure records, investigative documents and other reports shows that he played a central leadership role in the Republican power structure in the 1990s and early 2000s before becoming a wealthy media pundit and Washington consultant.

Santorum earned $1.3 million in 2010 and the first half of 2011, according to his most recent financial disclosure form. The largest chunk of his employment earnings — $332,000 — came from his work as a consultant for groups that advocate and lobby for industry interests, including a Pennsylvania energy company and the American Continental Group, a lobbying firm.

Santorum reported $400,000 in director’s fees and stock options as a board member of Universal Health Services, a hospital firm, as well as money from stints with Fox News, Salem Radio, and the conservative Ethics and Public Policy Center. His current income marks a stark contrast with his last year in the ­Senate, when he made about $190,000 in salary and book royalties.

Santorum has never registered as a lobbyist, a step that is required only if certain thresholds are met for the amount of time spent and contacts made on behalf of a customer. But even on the campaign trail, he has advocated for his former clients.

In Iowa in July 2010, for example, Santorum touted the importance of Marcellus Shale, a controversial source of natural gas. Just a month earlier, he had ended his three-year consultancy with Consol Energy, which has major hydraulic fracturing — or “fracking” — operations in the Marcellus Shale fields of Pennsylvania.

“It’s the largest natural gas [field] found in the history of the country, the second-largest natural gas field in the world,” he said. “It’s under Pennsylvania, and we are drilling, baby, drilling.”

Steve Ellis of Taxpayers for Common Sense, an advocacy group, said Santorum “occupied this gray area that’s become very popular for former lawmakers” to avoid having to declare themselves lobbyists. Former House speaker Newt Gingrich (Ga.), another GOP presidential candidate, also has come under fire for his consulting career.

“They provide strategic advice, they use their knowledge to help good-paying corporate clients,” Ellis said. “At some point, it becomes very questionable about whether this is lobbying. . . . If you have national ambitions, you want to avoid the scarlet letter of being a lobbyist.”

Santorum has alternately denied and defended his role in the K Street Project during his time in the Senate, according to news accounts. In 2005, he said the effort was “purely to make sure we have qualified applicants for positions that are in town.” A year later, as his reelection bid was in full swing, he said he had “absolutely nothing to do” with the project or one of its key creators, anti-tax crusader Grover Norquist.

“He was one of the central players in the K Street Project; he wasn’t just peripheral,” said Melanie Sloan, executive director of Citizens for Responsibility and Ethics in Washington, a watchdog group. “He’s trying to make himself a paragon of moral purity. But he was a huge part of pay-to-play politics during one of the dirtiest eras in Washington.”

Staff researcher Lucy Shackelford contributed to this report.