ALEXANDRIA, Minn. (AP) _ A retired farmer who admitted killing his wife to end her suffering from Alzheimer's disease wept as he asked a judge to place him in a nursing home instead of sending him to prison.

But the judge, apparently unmoved, on Thursday sentenced Oscar Carlson, 78, to serve at least 28 months of a 43-month prison sentence for the Feb. 29 shooting of his 71-year-old wife, Agnes, in an Evansville nursing home.

''I haven't got many years left, maybe not many days, either,'' Carlson said before sentencing, his voice faltering. ''I hope you will put me in a home, someplace where I can be of some good to somebody.''

Carlson told Douglas County District Judge Paul Ballard that he was ''so sorry'' for what happened to his wife of 45 years.

He was to begin serving his time at the Stillwater state prison as soon as his transfer could be arranged from the Douglas County jail, said defense attorney Michael Dolan.

''He's a frail old man placed in a system with violent people,'' said Dolan.

However, Douglas County Attorney Ann Carrott said, ''Justice was served by the fact he was imprisoned.''

With good behavior, Carlson would be eligible for parole in 28 months.

Carlson pleaded guilty several weeks ago to second-degree murder after Ballard said he would consider a prison sentence of no more than 43 months, or 28 months with good behavior. The agreement departs from state sentencing guidelines, which call for an 18-year sentence for second-degree murder.

Ms. Carrott opposed even the 43-month sentence. Although she said she felt compassion toward Carlson, she said she believes sentencing guidelines should be followed.

The prosecutor said defense attorneys did not confer with her on the plea arrangement, and said sentencing Carlson to anything less than 18 years would set a dangerous precedent.

However, Carlson's other attorney, Thomas Reif, said, ''We're talking about a man who's never even had a traffic ticket before this. I do not think sending him to prison at his age would serve society at all.''

During a pre-sentence hearing, Carlson said he snapped when he learned Feb. 28 that his wife had broken her hip and would have to be hospitalized. The next day, he took an old pistol to the Crestview Manor Nursing Home, and shot her four times.

''I just cracked up. I just couldn't take no more,'' Carlson said.

Relatives said the Carlson family was devastated by Mrs. Carlson's death, but had forgiven Carlson.

''He's still our father and we understand it was hard on him,'' said Mildred Penuel of Fargo, N.D., Carlson's youngest daughter.

Alzheimer's disease causes progressive memory loss and mental degeneration.