A man was found dead on a sidewalk in Northwest Washington yesterday morning in what officials said may be this winter's first death caused by hypothermia.

The frigid weather moved into the area Thursday night after snow blanketed the region. Homeless shelters swelled almost to capacity. Public libraries and dining rooms became bedrooms housing the homeless.

The cold continued all day, steady at about 21 degrees. The wind chill index was 11 degrees below zero, making Washington feel colder yesterday than Moscow, Stockholm and Fairbanks, Alaska. Temperatures below the freezing mark are expected to last through the weekend.

Last night, advocates for the homeless drove through the District, hoping to give a blanket and a warm bed to someone like Melvin Lewis Wharton, 51, who may have died from exposure. Wharton was discovered by a person walking home about 2:30 a.m. in the 2900 block of 11th Street NW. No home address has been found for him, but it is typical that someone who died outside had no place to go, police said.

Wharton was wearing a black hat, boots, sweat pants and a brown coat but no shirt when he was found in 22-degree weather, police said. The wind chill made it feel like 8 degrees below zero around the time he was found, said Mark Tobin, a meteorologist with AccuWeather Inc.

There were no signs of foul play or trauma on his body, which was taken to the medical examiner's office. Though it appears Wharton died of exposure, tests after the autopsy will confirm the cause of death, said D.C. Medical Examiner Jonathan L. Arden.

The District enacts a hypothermia alert plan when the temperature or wind chill index hits 32 degrees or below, and shelters open overnight, said Jean Barton, lead shift supervisor for the D.C. Hypothermia Hotline.

The District has the capacity to house 2,600 people in its shelters, a count that has not been exceeded this winter.

Because the District has been sporadically chilled to hypothermia-inducing lows, overflow shelters at the Reeves Municipal Center at 14th and U streets NW and at 2 D.C. Village Lane SW have been open the past two weeks, said Barbara Childs, deputy director for operations of the District's Emergency Management Agency.

A call to the hot line at 1-800-535-7252 will garner a ride to one of the city's seven emergency shelters. Barton also encourages residents who spot homeless people on District streets to call the hot line, and a van will be dispatched to offer assistance.

In Montgomery County, shelters were brimming with people seeking refuge from the cold, and officials said they were struggling to uphold their policy of turning no one away.

"In the past few days, we're squeezing the walls, all of us, to fit people in," said Sharan London, executive director of the Montgomery County Coalition for the Homeless.

To help those who need to stay warm over the weekend, the Progress Place center in Silver Spring will be open to the public during the day, London said.

One of the trailers in Rockville that the county uses for homeless men has become an impromptu infirmary to handle flu cases, London said.

"Despite a big campaign and giving people hundreds of flu shots, we've got a lot of people sick with it," she said.

Several advocates for the homeless said that Montgomery County transportation officials have had a shortage of bus tokens, making it difficult at times to get people from Silver Spring, where most of those in need of shelter are, to Rockville, where the shelters are.

Prince George's County's three shelters have not been unusually busy, officials there say, because during small stretches of cold weather, family members and acquaintances are usually more willing to take in the homeless, according to Tim Jansen, director of community services.

Social services officials in Prince William County responded to this week's frigid weather by extending the hours of the county's winter homeless shelter, offering round-the-clock warmth to those who seek shelter in the woods.

Debra Danieley, the county's director of homeless services, said yesterday that the shelter has been at capacity since the cold spell hit. Other Prince William homeless services groups have canvassed known campsites in wooded areas in an attempt to encourage the homeless to seek shelter.

"As long as we are having these lethal temperatures, we will stay open as much as possible," Danieley said. "When it gets this cold, it gets very dangerous for people to be out on the streets and in the woods."

At the Eleanor U. Kennedy Shelter on Route 1 in the Fort Belvoir section of Fairfax County, the demand for shelter was so high Thursday night that more than a dozen people had to sleep in the facility's dining room. The shelter has 50 beds and room for 15 more, but in recent days that hasn't been enough, said Diana Ventry, a caseworker. The county-run facility is the only shelter on Route 1 and cannot turn anyone away.

With the increased demand, Ventry appealed for community support in helping provide hot meals and donating warm clothing, especially thick socks, gloves, hats and coats.

"We have people coming in with just sweaters on," she said.

In Arlington, the emergency shelter on North 15th Street was full Thursday night, but not overflowing, though county officials were bracing for an onslaught over the weekend. The 40-bed facility had 42 users Thursday.

Staff writers Peter Pae, Fern Shen and Josh White contributed to this report.

CAPTION: Hypothermia crew members Jean Barton and Ralph Winchester offer blankets, socks and gloves as well as a ride to a shelter to James Majors on a steam grate in Northwest Washington. He turned down the ride and accepted gloves.

CAPTION: Hypothermia van crew members Ralph Winchester and Jean Barton give blankets and socks to a homeless woman at 17th and D streets NW. She refused a ride to a shelter despite last night's freeze.