A Bozeman man who drove a bus full of Bozeman middle school students into Yellowstone National Park while under the influence of alcohol pleaded guilty Thursday in federal court in Mammoth Hot Springs.

Kevin Leon Stark pleaded guilty to operating a commercial vehicle with “a detectable amount of alcohol” before U.S. Magistrate Judge Stephen E. Cole, according to court documents.

Stark admitted to having an alcohol level of 0.032, a federal prosecutor said Thursday after the hearing.

Though the legal limit for passenger-vehicle drivers is 0.08 in Montana, it is 0.04 for commercial drivers.

Stark and Jack Parrent of Bozeman were arrested June 3, while working for Karst Stage, after they drove their buses loaded with Sacajawea Middle School students into Yellowstone National Park after a night of heavy drinking, according to charging documents. The two no longer work for the transportation company.

Parrent’s blood-alcohol content — tested sometime after 7 a.m. when a park ranger saw his bus swerving over the centerline — was 0.12, according to court records.

Court records indicate Parrent had been convicted for drunken driving at least three previous times.

Both men were initially charged with reckless endangerment and operating a commercial vehicle with a detectable amount of alcohol.

Parrent was also charged with drunken driving and Stark with recklessly creating a risk of public jeopardy. All the charges are misdemeanors.

According to the court document filed Thursday, Stark’s charges of reckless endangerment and recklessly creating a risk of public jeopardy will be dismissed at his sentencing hearing scheduled for Jan. 11.

Parrent is scheduled to be tried next week and Stark “is expected to testify against Parrent,” the federal prosecutor said.

Stark’s conviction carries a maximum sentence of six months in jail and a $5,000 fine.

But prosecutors will recommend 30 days in jail, one year unsupervised probation and a $750 fine, the federal prosecutor said. He will also ask the judge to ban Stark from entering Yellowstone National Park until he completes his sentence.

Jodi Hausen can be reached at jhausen@dailychronicle.com or 582-2630.