DENVER (AP) _ An Army nurse who says she is being punished for fighting racial discrimination began a one-year prison sentence Tuesday for being disrespectful, disobedient and disorderly.

Second Lt. Mary Rahming, 35, the only black officer in the cardiology- general medicine ward at Fitzsimons Army Medical Center, will spend a short time in detention at Fort Carson in Colorado Springs, then be transferred to the federal prison at Fort Leavenworth, Kan., military officials said.

Rahming said the charges were filed because she alleged racial discrimination and harassment by her superiors.

Fort Carson Staff Judge Advocate Col. Howard Eggers said Rahming will receive her $1,260 monthly salary until her final appeal. Military authorities said she would be dismissed from duty after serving her sentence.

Rahming was commissioned by the Army in March 1986 and less than a year ago received the highest marks possible on an officer evaluation.

A court martial found her guilty on Dec. 22 of four counts of being disrespectful to a superior commanding officer, two counts of unlawful disobedience, one count of disorderly conduct, and one count of failure to report for duty on time 15 times.

Specific charges included tardiness, hanging up on a major during a telephone conversation and throwing a urine sample on the restroom floor.

Rahming refused an offer to resign instead of facing the court martial.

She said that in July 1987 she found a Ku Klux Klan ''on the March Again'' poster in her mailbox at work. She filed a formal complaint with the medical center's Equal Opportunity Office against Capt. Laurie McNabb, head nurse at the hospital, section chief Lt. Col. Lanne Spencer and Department of Nursing Chief Col. Rita Vanlith.

Military officials said investigations found no evidence of racial discrimination against Rahming.

Eggers said he had never seen an officer get a prison sentence for similar offenses.

''I think the judge was impressed with the number of offenses and the length of time supervisors took in an effort to encourage better behavior,'' he said.

Maj. Gen. James Hall, Fort Carson commander and a black, will review the case in February. Hall has the power to reduce Rahming's sentence.