Barnett, appearing for the first time before a panel looking into recruiting practices at the school, said there were 10 people at the off-campus party, including four football players.
"There is no question in my mind that inappropriate behavior occurred," Barnett said. "There is no question that the behavior of the 10 young people involved was the result of their own poor decisions and under the influence of alcohol."
Three women have said they were raped by players or recruits at the party or just afterward. They have sued the school in federal court, seeking unspecified damages for what they say was the school's failure to rein in athletes and provide equal protection to women.
At least eight women since 1997 have accused Colorado football athletes of rape, though no charges have been filed.
The Board of Regents' panel is to issue a report at the end of the month on whether Colorado uses sex and alcohol to entice recruits to the Boulder campus. A separate investigation headed by the state attorney general is under way.
Barnett was put on paid leave for comments he made about two of the alleged rape cases, including that of Katie Hnida, a former kicker who said she was raped by a Colorado teammate in 2000.
Barnett has said his statements were taken out of context - he was answering questions about why she left Colorado to later enroll at New Mexico - and that he and the university tried to make her feel welcome.
A few hours before Barnett spoke, the panel released a March 30 e-mail to a commission attorney from Dr. David Hnida, the woman's father, an Army surgeon posted in Iraq.
Hnida said Barnett and other university officials must have known about sexual harassment problems his daughter was having before she left Colorado.
"We both have been distressed at the information we read coming from the university, as well as Gary Barnett," David Hnida wrote. "To be blunt, there is quite a bit of lying and deception right now."
He said his daughter would be willing to speak to the panel after spring football practice at New Mexico ends Thursday.
In his statement to the panel, Barnett gestured at times with his hands and raised his voice to make a point. He said every accusation against him and his coaches is untrue, saying he believes they can "can restore accurate public perceptions about our dignity and our integrity."
He said he feels a strong sense of responsibility not only for his players' performance on the field but their behavior in the community, and tries to make them understand they have no more rights or privileges than other students.
But he said there are limits to tracking the activities of dozens of players, and "I can't live their lives for them."
Kathy Redmond, founder of the National Coalition Against Violent Athletes, told the panel Monday that a "rape culture" exists within Colorado's sports programs.
"Players are taught that women are objects, commodities, and that if you come to this school, you get women, you get sex," said Redmond, who received a $50,000 settlement from the University of Nebraska after she accused a football player of rape in 1991. The player was never charged.
Redmond said university leaders should be replaced because they ignored problems.