Hollywood actor Felicity Huffman has had her bond set at $US250,000 ($A353,000) after appearing in court charged over what the US Department of Justice has labelled as the biggest college admissions scam ever prosecuted in American history.

Huffman, an Academy Award nominee and Desperate Housewives star, appeared in court in Los Angeles on Wednesday (Australian time) to face charges of conspiring to commit mail fraud and honest services mail fraud.

Her husband, actor William H. Macy, was in court and jotted notes during the hearing.

Among the 50 people also charged in the case, which has ensnared celebrities, real estate moguls, high-ranking CEO’s, a global law firm and a fashion designer, are Full House star Lori Loughlin and her husband, fashion designer Mossimo Giannulli.

Giannulli’s bond was set at $US1 million when he appeared in court on Wednesday. He has surrendered his passport and his travel is restricted to the US (the same restrictions were imposed on Huffman).

Loughlin was not in court with him.

Felicity Huffman waits in a corridor ahead of her Los Angeles court appearance. Photo: AAP

Prosecutors allege the most sweeping college admissions scheme ever unearthed in the US was masterminded at a small college-preparation company based in Newport Beach, California.

It relied on bribes to coaches, false test takers and doctored photos misrepresenting non-athletic applicants as elite competitors to gain admissions for the children of rich parents.

“These parents are a catalogue of wealth and privilege,” Andrew Lelling, the US attorney in Boston, said. “For every student admitted through fraud, an honest, genuinely talented student was rejected.”

William “Rick” Singer, 58, pleaded guilty on Tuesday to charges related to running the scheme through his Edge College & Career Network. It charged from $100,000 to as much as $2.5 million per child for the services, which were masked as contributions to a scam charity Singer runs.

“I was essentially buying or bribing the coaches for a spot,” Singer said as he pleaded guilty to charges including racketeering, money laundering and obstruction of justice. “That occurred very frequently.”

John Vandemoor, a former Stanford University sailing coach who worked with Singer, also pleaded guilty to racketeering conspiracy.

Some 300 law enforcement agents swept across the US to make arrests in what agents code-named Operation Varsity Blues.

Prosecutors have so far named 33 parents, 13 coaches and associates of Singer’s business.

Representatives for Huffman, Loughlin and the companies involved either declined to comment or did not respond to requests for comment.

The alleged masterminds of scam and involved parents could all face up to 20 years in prison if convicted.

-with AAP