(Reuters) - In an attempt to deflect attention over his involvement with Freddie Mac, Republican presidential candidate Newt Gingrich's former consulting firm on Monday released a contract he had with the troubled mortgage firm.

The 16-page document covered a consulting agreement only for work done in 2006 and shed little light on Gingrich's duties. The document calls for a $25,000-a-month in fees for the year.

In total, Gingrich was paid between $1.6 million and $1.8 million in consulting fees for eight years of work with the lender, according to previous disclosures.

The deal sparked criticism of Gingrich as a Washington insider but he has insisted his arrangement included no lobbying and that he was paid for his historical acumen.

His rivals for the Republican presidential nomination, particularly Mitt Romney, have seized on his relationship with Freddie Mac, charging him with reaping monetary benefits for his influence in Washington.

When the form was released, Romney senior adviser Eric Fehrnstrom tweeted: Newt's K Street firm finally released the Freddie contract, but only for 2006. Where are missing years? He started there in 99.

Attacks against Gingrich's ties with Freddie intensified following his stunning victory over Romney in Saturday's South Carolina primary.

The contract agreement states that part of his duty was to perform services in a highly professional manner consistent with the quality provided by other top firms providing comparable services in the Washington, D.C., metropolitan area.

Romney on Monday challenged Gingrich to describe in detail the work he performed and return the money he made. His campaign released a television ad attacking Gingrich's Freddie Mac ties and linking them to Florida, which has been particularly hard-hit by the housing market crash.

While Florida families lost everything in the housing crisis, Newt Gingrich cashed in, the ad says.

Republicans blame government-sponsored mortgage finance companies like Freddie Mac and Fannie Mae for the 2007 housing-market crash that plunged the country into the deepest recession since the 1930s. Outside economists say lax oversight of the financial industry is primarily to blame.

The Center for Health Transformation, a consulting firm founded by Gingrich in 2003 and sold to his partners in 2011, has previously said that it could not release the Freddie Mac contract due to client confidentiality concerns.

The company says it does not perform lobbying services for clients, which come from the healthcare, education and technology industries.

(Additional reporting by Deborah Charles and Steve Holland; Editing by Marilyn W. Thompson and Bill Trott)