CAMBRIDGE, Mass. — The actress Lori Loughlin and her husband, Mossimo Giannulli, a fashion designer, have pleaded not guilty to new bribery charges prosecutors have brought against them in the college admissions scandal, signaling that they intend, at least for now, to keep fighting the case.

Prosecutor have accused Ms. Loughlin and Mr. Giannulli of paying $500,000 to get their two daughters designated as recruits to the University of Southern California women’s crew team as a way to ensure their admission to the school.

The couple have maintained their innocence, even as Hollywood gossip magazines have reported that Ms. Loughlin is increasingly worried about what will happen. In contrast, the other Hollywood actress ensnared in the case, Felicity Huffman, who was accused of paying $15,000 to cheat on her daughter’s SAT, pleaded guilty and has already completed her prison sentence. (Ms. Huffman was sentenced to 14 days, but served only 12, including the day she was arrested.)

Prosecutors originally charged roughly three dozen parents arrested in the case with one count of conspiracy to commit mail fraud and honest services mail fraud. After Ms. Huffman and roughly a dozen other parents agreed to plead to that count, prosecutors added money laundering charges against the remaining parents, including Ms. Loughlin and Mr. Giannulli. Then, last week, they added the new charge, of federal programs bribery, which can carry a sentence of up to five years in prison.

Lawyers involved in the case have said prosecutors brought the new charges in part out of frustration with the sentences given out in the case so far, which have ranged from probation to five months in prison, and have all been less than what prosecutors had asked for.