A 43-year-old Washington man who has spent 23 years in prisons was sentenced here yesterday to 20 years without parole under the new federal Career Criminal Act for shooting up his estranged wife's Southeast apartment last summer.

Frederick Jackson, formerly of a Southern Avenue SE address, is the second man in the District to be sentenced under the act, which sets a mandatory minimum sentence of 15 years for persons convicted of a firearms violation who have three or more prior burglary or robbery convictions.

U.S. District Judge Thomas P. Jackson imposed the sentence despite arguments from defense attorney Robert Price that there had been a "substantial and dramatic change" in Frederick Jackson since he committed the crimes that define him as a "career criminal" under the new law.

"The record of 15 years ago may not tell the court about Mr. Jackson today," Price said. Court documents show Jackson was convicted in 1965 and 1973 of robbery and in 1973 of bank robbery and armed robbery.

Price said Jackson was released in 1984 and had been on his own about 11 months when he was arrested last July and charged in connection with the shooting incident. Jackson was alone at the apartment at the time of the shooting, and no one was injured.

Price told the judge that Jackson had been adjusting well to life outside prison and that he had married and was working. Price also offered a letter from a Lorton Reformatory corrections officer who said Jackson had done well in prison.

"I don't believe that the man has been given a chance," Price said.

Judge Jackson responded that the defendant "has a criminal record dating from the age of 12" and that he "had been released again and again but evidenced the best citizenship when he was incarcerated."

At the time of the shooting incident, Jackson was free on bond after being arrested for possession of heroin with intent to distribute, according to a sentencing memorandum.

Jackson, who has been in jail since his shooting arrest, was sentenced Feb. 25 by a D.C. Superior Court judge to five to 15 years in prison on the drug charge.

Clendon Lee, a spokesman for the U.S. Attorney's office, said Jackson was arrested July 12 after the shooting incident, which left five bullet holes in the doors of his estranged wife's apartment at 2707 Shipley Ter. SE.

Assistant U.S. Attorney Zinora Mitchell told the judge that the "community deserves the kind of protection" offered by a lengthy sentence.

"That's preposterous," Price said. " . . . He was in an apartment, not shooting at anyone. . . . I don't think that's what justice is all about."