GOP candidate Newt Gingrich, who has said he never lobbied on behalf of his consulting clients, reported to a top lobbyist with Freddie Mac as part of a $25,000-a-month contract, according to records released late Monday.

The one-year contract overseen by Freddie Mac executive Craig Thomas represents only a portion of the former House speaker’s long relationship with the mortgage giant, which spanned eight years and resulted in at least $1.6 million in fees for Gingrich’s empire.

The partial documentation also appears unlikely to quell escalating demands from GOP rival Mitt Romney, who has sharply criticized Gingrich for his lucrative career collecting tens of millions of dollars in fees from Freddie Mac, health-care firms and other clients.

The attacks, repeated in Monday night’s presidential debate, are part of an attempt by Romney to blunt Gingrich’s momentum after a commanding primary victory in South Carolina on Saturday. A new ad from the Romney campaign alleges that Gingrich “cashed in” on the housing meltdown by taking money “from the scandal-ridden agency that helped create the crisis.”

The 15 pages of documents released late Monday consisted primarily of contractual boilerplate, along with signature pages laying out the $300,000 annual fee. The “scope of services and fees” consists of a single paragraph with no details.

The Gingrich campaign did not respond to a request for comment on whether it planned to release any more Freddie Mac records.

Gingrich has offered varying explanations for his ties to the mortgage company, initially claiming he was hired as a “historian” and later characterizing himself as a strategic adviser. Gingrich and his supporters have repeatedly denied that he acted as a lobbyist for Freddie Mac or any other client.

“If you read the contract,” Gingrich said in Monday’s debate, “. . . I was supposed to do consulting work. There is no place in the contract that provides for lobbying.”

Thomas, who at the time was director of public policy at Freddie Mac, was identified as the “project director” in the Gingrich contract. Thomas was listed as a lobbyist for Freddie Mac in 2000, 2005 and 2006, according to disclosure records.

The Freddie Mac contract is part of a series of tit-for-tat releases between Gingrich and Romney, who is releasing his 2010 tax returns after withering attacks from Gingrich on the issue. Gingrich released records last week showing that he and his wife paid an effective federal tax rate of about 32 percent on income of $3.14 million.

Gingrich has been dogged for months by questions about his lucrative consulting contracts with Freddie Mac, a government-sponsored mortgage company that is viewed by many conservatives as a prime cause of the housing crisis. Gingrich has said he warned the company about its “insane” lending practices.

Bloomberg News reported that Gingrich had earned up to $1.8 million from Freddie Mac from 1999 to 2008 to build support among Republicans for its private-public business model. The Gingrich campaign disputed portions of the report, but resisted releasing any documents from the arrangement until now.

In an explanation on its Web site, the Gingrich campaign says that “at no time did Gingrich lobby for Freddie Mac,” nor did he “ever advocate against pending legislation affecting Freddie Mac.” The campaign said Gingrich “offered strategic advice” to Freddie Mac and a “very wide range of clients” through his consulting firm.

Gingrich also repeatedly sought to play down his personal role in the contract, suggesting in one interview that he only spent about an hour a month talking with Freddie Mac officials.

The Freddie Mac contracts were just a small part of a vast financial empire, often dubbed Newt Inc., assembled over the past decade. The private and nonprofit groups led by Gingrich brought in an estimated $150 million since he left Congress.

One entity, a think tank called the Center for Health Transformation, collected dues of up to $200,000 per year from insurers, hospitals and other health-care firms in exchange for “access to Newt Gingrich” and political advice, according to records and interviews.