Jeffrey Todd Dyson, the Fairfax man arrested and charged Tuesday night with the May 7 Old Town slaying of Robert H. Land, probably was invited into Land's home on the day of the slaying, Alexandria police said yesterday.

Dyson, 23, and Land, 72, a retired Library of Congress official who was found strangled in his condominum apartment, were seen together at the Bellehaven Marina the morning Land was killed, police said.

"We knew that both men frequented the areas along the George Washington Parkway," Homicide Capt. Andre Salvas said yesterday.

In July 1984, Dyson was released from Fairfax County Jail, where he had been serving a seven-year sentence, with three years suspended, for burglary. On Nov. 30, he was ordered to serve a year in the state penitentiary because of a parole violation. Neither Alexandria nor Fairfax County police could say yesterday why Dyson had not begun to serve that term.

After Dyson was released from the Fairfax County Jail, he was to have been picked up by District police for another crime, but was not, an Alexandria police spokesman said yesterday.

The vital clue in the Land case was a green and white Chevrolet seen near Land's home the morning he was killed. A similar car was seen near the marina that morning, according to police. They said Dyson, of 2729 Fairhaven Ave. in the Huntington section of Fairfax, owns a car of the same description.

Land was found by his daughter at his condominium on 601 Wilkes St. about 12:30 p.m. on May 7. He had been assaulted shortly after he returned to his apartment from a small garden he tended in the neighborhood, police said.

The apartment was in disarray and some items were taken, but there was no sign of forced entry, police said.

Friends described Land -- a passionate gardener who had hundreds of tulips in his back yard -- as gentle, learned and enthusiastic. He did not appear to have met Dyson before the day of the killing, police said.

Land had apparently been deeply troubled by the illness of his wife, Elizabeth, who was in the hospital for hip surgery at the time of his death, friends said. "They were like two seagulls and he was under a lot of stress when it happened," according to one neighbor. "They were very close."

Dyson is being held without bond in the Alexandria Correctional Center. A trial date will be set on Wednesday.

Dyson appeared in Alexandria Circuit Court yesterday, but spoke only to tell the judge that he could not afford a lawyer and would like one to be appointed to represent him.