A 72-year-old retired Library of Congress official was found slain in his Old Town Alexandria condominium yesterday, shocking residents of the quiet neighborhood, Alexandria police said.

Robert H. Land, who retired several years ago as a top official in the library's reference department, was found by his daughter about 12:30 p.m. yesterday in his condominium at 601 Wilkes St., police said. They said he apparently was strangled.

The apartment was in disarray but police officials declined to say whether robbery was the motive. They are investigating whether items are missing from the third-floor residence in the brick building of a well-to-do section of the city, said Lucy Crockett, spokesman for the city police department.

Police declined to provide details of the homicide, including the name of the daughter who found the body and whether they have any suspects.

The victim's widow, Elizabeth (Bootsie) Land, was one of the first women on the Alexandria School Board, serving in the 1960s and early 1970s. She broke her hip recently and has been in a hospital for the last several days, neighbors said.

Friends described Land, a Civil War and colonial history buff, as a quiet and kindly man who tended a small garden nearby and offered friends tomatoes.

"We're very shocked," said Libby Curtis, a neighbor of the Lands in the four-story, heavily secured brick complex, Tannery House. "He was a delightful gentleman, and a very fine neighbor."

Other residents said that that area of southern Old Town has little street crime, and that their building has multiple locks. One neighbor noted that the Lands had a triple lock on their door.

While neighbors said violent crime is rare in that area, murders there have been well publicized. In February 1984, several blocks from the Lands, real estate dealer Elizabeth Elliott, 68, and her companion, Karl von Lewinski, 71, were stabbed to death in their apartment. A tenant, George Alec Robinson, was convicted of murder and last July was sentenced to four consecutive life terms.