The calls started reaching their offices around 1 p.m.; by midafternoon most of the residents of a building at the Larchdale Woods apartments on Larchdale Road in Laurel had gotten the word: Come home. Your building has been condemned.

"They said the wall fell down," Elaine Upson recalled last night as she packed her coffeepot and five days' worth of clothing and headed for a hotel.

The wall -- 10 feet by 9 feet in a basement utility room -- collapsed about 10:30 a.m., smashing a natural gas valve serving a water heater but injuring no one, according to Prince George's County housing and fire officials. The apartment building, with entrances at 11317 and 11319 Larchdale Rd., was cordoned off.

County fire officials said a crack in the four-story building's cinder block foundation threatened the safety of its occupants and forced housing inspectors to shut down the building. The building was occupied by 27 people in 22 apartments; six other apartments were vacant.

It was unclear last night how long the building will be closed or what specific dangers are involved. State inspectors are scheduled to investigate this week, resident manager Margaret Lambert said.

Maintenance officials at the complex said they were doing a routine check in nearby buildings when the wall crumbled. "We got down there fast enough to cut the gas off before it blew, thank God," said supervisor Dan McDonald

Residents were told to take enough belongings for at least five days and were cautioned against trying to move heavy furniture because of the instability of the building.

The county's Office of Emergency Preparedness arranged for most of the tenants to stay at a Howard Johnson's motel off Rte. 202 in Hyattsville at county expense. Three families were able to move into unoccupied apartments in the 526-unit Larchdale Woods complex.

The 22-year-old development is owned and operated by Preferred Financial Corp. of Tarzania, Calif., according to Lambert.

Most of the residents said last night they were away when the wall crumbled. Those who were at home said they heard nothing. "We were on our way out and we saw the fire trucks," said Terry Proctor, who spent the morning in her third-story apartment with her 10-month-old daughter Jennifer. "That's when I heard about it." Proctor said she and her husband plan to stay with her sister in College Park.

Tenants were allowed to removed belongings until 10 p.m. Maintenance workers were expected to start shoring up the walls and the ceiling of the utility room afterward. They also planned to fill in a hole -- three feet wide by 10 feet deep -- outside the building near the collapsed wall.