A 22-year-old Phi Beta Kappa graduate of Hollins College who was an employe of The Washington Post was found shot to death in the foyer of her new apartment yesterday in a case that apparently left police with few clues or leads.

Mary Lazarou, an editorial aide who worked in The Post's library, was found about 6:45 p.m. by coworkers who arrived at the victim's apartment a few blocks from the newspaper carrying supplies for a housewarming party.

Lazarou had finished moving only on Wednesday to her fourth-floor efficiency apartment in the 10-story, red brick building at 1325 15th St. NW.

Police were called almost immediately after the body was found on the carpeted floor just beyond the front door of the apartment, in which Lazarou lived alone.

For several hours last night, investigators interviewed witnesses and searched the apartment and its surroundings for fingerprints or other evidence. Homicide detectives said later that they had found no sign of forced entry to the apartment and that they knew of no motive for the slaying.

One detective said the shooting might have occurred after the assailant had been in the apartment for some time. But it was also possible, the investigator said, that Lazarou was shot as she answered a knock at the door.

Shocked coworkers described Lazarou last night as sweet, pleasant, helpful and extremely good-natured.

"She was one of the loveliest" women ever to work at The Post, said Mark Hannan, the newspaper's director of research and Lazarou's supervisor.

"She was quiet, brilliant and had a great sense of humor," he said.

Lazarou, who attended Wakefield High School in Arlington, graduated last year from Hollins College in southwest Virginia with a major in history and French, which she spoke fluently. After holding summer and part-time jobs at The Post last year and in 1980, she became a full-time employe early this year.

Her job involved preparing material for a computerized information retrieval system.

Until moving to her new apartment this week, she had lived in another apartment near the newspaper with her mother, Lucy, who had worked for The Post for about eight years.

The new apartment building, The Latrobe, at the corner of 15th Street and Rhode Island Avenue NW, is entered through a vestibule on 15th Street, which leads to two heavy glass doors that are secured by a lock.

Residents can open the door for visitors by operating a buzzer after they have been called from a special telephone in the vestibule. One of the unanswered questions last night was how the assailant might have entered the building.

Lazarou, who reported for work as usual yesterday, apparently returned to her new apartment sometime before 5 p.m., when a building employe saw her come downstairs to pick up a package.

Her coworkers arrived at the building around 6:30 p.m. They telephoned her apartment from the vestibule, but got no response, and were admitted by a building employe. They took the elevator to the fourth floor, walked directly across a corridor and knocked on the victim's door. There was no answer.

Finally, they tried the door. It was unlocked and they opened it.

Lazarou was lying on the floor, fully clothed and stained with blood. Her friends found no sign of life and summoned police. A member of the medical examiner's office pronounced Lazarou dead in her apartment.

Investigators said she had been shot once in the head.

There was no indication whether anything had been taken from the apartment. Several residents interviewed last night said they had not seen or heard anything unusual.