While other emergency shelters in Northern Virginia opened their doors to the homeless Monday night, when temperatures dipped to 23 degrees, more stringent policies in Arlington County allowed a similiar facility to remain closed.

A national advocate for the homeless said yesterday that Arlington's policy is strict and could endanger the welfare of some of the county's homeless.

"The bottom line is that not many of us keep the thermostat set at 26 degrees," said Joan Alker, director of the National Coalition for the Homeless. "If people are freezing and want not to sleep on the street, in any civilized society that request should not be turned down."

Guidelines allow officials of the Department of Health and Human Services to open the shelter when weather conditions are deemed by county officials to be "life-threatening." Ron Carlee, the department's director, defined life-threatening as temperatures below 25 degrees, a wind chill of zero or precipitation in combination with cold weather.

"It's a humanitarian gesture," Carlee said yesterday. "What we have to offer is better than people freezing to death out on the street."

Arlington's emergency shelter, which uses county-owned office space, can accommodate up to 18 people and is operated by volunteers from the Red Cross. People who use the shelter must be referred by law enforcement or mental health officials.

Officials in Alexandria yesterday said emergency beds have been set aside throughout the winter, regardless of the temperature. Fifteen additional spaces have been set aside at each of three shelters in Fairfax County to cope with emergency cases there all winter, officials said.

In Alexandria and Fairfax, officials said life-threatening weather conditions start at 32 degrees -- 7 degrees warmer than what Arlington officials consider to be dangerous.

"There's not a lot of empirical information on cold's effect on the human body and when you reach hypothermia," said Ray Spicer, who coordinates homeless programs in Arlington.

Until this winter, Arlington did not have a cold-weather shelter, officials said, and referred homeless clients to the Carpenter Shelter in Alexandria. Arlington officials said they lost that option when that shelter moved last year.

Carlee said the decision about whether to open the shelter is made daily, depending on the temperature and how long a cold snap is expected to last. County Manager Anton S. Gardner makes the decision, based on a recommendation from Carlee.

Carlee said most of the individuals who go to the emergency shelter fail to qualify for admission to Arlington's other four shelters, because of substance abuse problems or failure to demonstrate a concerted effort to find work or housing. The other shelters are for homeless people who are seeking employment or public housing, he said.

Because last night was the third consecutive night with freezing temperatures, the shelter opened, Carlee said. Even then, he said, the decision was "a close call."