The newspaper said the 21-year-old son of Hall of Fame quarterback Joe Montana pleaded guilty June 23 and was ordered to pay $435 in fines and court fees. He also was ordered to complete a chemical dependency program and his driver's license was suspended for six months for refusing to take a breath test.
A 90-day jail sentence was suspended.
Montana's plea to the lesser charger came after the Missoula County attorney's office found he did not perform poorly enough on sobriety tests to warrant the DUI charge.
Montana dropped a request to have his license restored, the newspaper said.
Montana is considered in contention for starting quarterback after transferring to the Grizzlies' program from Notre Dame in February.
He was among 11 Irish athletes arrested in South Bend, Ind., on misdemeanor charges of underage drinking at a party last July.