A District man pleaded guilty to first-degree murder yesterday in the strangulation last year of an aide in Mayor Marion Barry's reelection campaign.

Kenneth D. Hubbard acknowledged to a D.C. Superior Court judge that he killed Peggy Russell Gee, 55, "with my hands" and sodomized the campaign scheduler after entering Gee's Northeast house to get her golden retriever.

Gee's nearly nude body was found in the early morning hours of June 14, 1986, by firefighters called to her burning and ransacked home at 4209 18th St. NE. They found three separate fires, including one in the dining room set on top of a carpet rolled around Gee's upper body.

A D.C. medical examiner said Gee apparently had died before the fires were set.

It is highly unusual for a defendant to plead guilty to first-degree murder, which carries a mandatory prison term of at least 20 years, but prosecutors said yesterday that the physical evidence against the 27-year-old Hubbard was "overwhelming." Hubbard also pleaded guilty to burglary and attempted sodomy.

Prosecutor Terence J. Keeney told Judge Reggie B. Walton that blood found on Gee's blouse matched Hubbard's and was an especially rare blood type. In addition, Keeney said a dental impression of Hubbard's teeth matched a bite mark on Gee's breast, that fibers taken from Hubbard's shoes matched those of Gee's carpet and that a turquoise dress sash found in a sink of bloody water in Hubbard's house belonged to one of Gee's dresses. He also said a head hair consistent with Gee's was found on a pillowcase.

No motive was described in the court proceedings, but prosecutor Keeney told the judge that Hubbard, who lived five blocks away, had removed Gee's dog from her yard at least twice in the two months before the murder and attempted unsuccessfully to seek a reward from Gee for the dog's return.

Keeney said that shortly before the murder, Hubbard, who has a history of substance abuse, was drinking with some friends at a liquor store not far from Gee's house.

When the judge asked Hubbard why he had gone into Gee's house that night, Hubbard answered quietly "to get the dog."

In exchange for Hubbard's pleading guilty, the government agreed to dismiss other charges against him, including arson, robbery and destruction of property. Hubbard faces a maximum prison term of 30 1/3 years to life.

Greta Van Susteren, Hubbard's lawyer, said after the court proceedings that her client "feels a tremendous amount of remorse" and "from the beginning was ready to acknowledge his responsibility." In an unusual legal skirmish, prosecutors withdrew a first-degree murder plea offer in April after Hubbard already had accepted it and insisted he also plead to some of the additional charges.

Sources said yesterday that Hubbard had decided to plead guilty after two psychiatrists who examined him for a possible insanity defense concluded that he was not insane.

Hubbard was sent to St. Elizabeths Hospital for a mental evaluation the month before Gee's murder after he barricaded himself inside his house.