The number of Hurricane Katrina survivors in the Washington region has tripled since Friday, swelling to more than 4,000 through a steady flow of displaced people, according to Red Cross and local officials.

In Northern Virginia, more than 900 are receiving aid from the Red Cross in Fairfax and Loudoun counties, up from 560 last week.

In Maryland, the largest increase is in Prince George's County, where Red Cross officials reported that 833 evacuees had registered with the agency, up from the 352 who had registered Friday.

"I'm totally surprised," said Linda Frazier, director for emergency services for the Red Cross office in Hyattsville. "I had not anticipated so many coming here. We don't have a shelter open."

The overall number of evacuees in the region probably is even higher because many displaced people have yet to tap into the social services network. Others are receiving help from relatives or other private sources, said Red Cross and county officials. In Montgomery County, for example, the number of known evacuees was 567, up from about 200 Friday. But officials said yesterday that they believe as many as 600 are in the county.

"We are confident there are more here," said David Weaver, a spokesman for Montgomery County Executive Douglas M. Duncan (D).

Hundreds of the displaced are seeking services in nearly every county in Maryland and Virginia, including outer suburban counties such as Frederick, Howard, Anne Arundel and those in Southern Maryland, according to Red Cross officials in those areas.

It's unclear how many displaced families may have sought services in more than one county. Officials at the Red Cross, the main agency providing help, said their offices are connected to a single database, so they don't believe there's much duplication.

"We have safeguards against that," said Cameron Ballantyne, a Red Cross spokesman for the region.

About the only place the number is decreasing seems to be the D.C. Armory. Yesterday, the office of Mayor Anthony A. Williams (D) said fewer than 150 people were living there, about half the number that arrived aboard two planes a week ago.

Many have moved in with relatives, friends or church groups in the region, and an additional 20 are expected to move into temporary housing soon, officials said.

Frazier said most new arrivals are staying with relatives, friends, church groups and families who have volunteered to host victims.

Weaver said the official count of displaced people here had climbed as more victims turned up at Red Cross centers, where they can receive myriad services, from food stamps to health screenings.

"We have made it easier for them to access support services, and in the process we've gotten a handle on just how many people are here," Weaver said.

He added that the county, the Red Cross and faith-based groups were working together and were adequately prepared to support the rising volume of displaced. He noted that Duncan had promised to house 1,000 evacuees.

"We are prepared to take even more," Weaver said.

Yesterday, Duncan announced that the Montgomery County Crisis Center will serve as a one-stop service center for evacuees. There, they can get help obtaining food stamps, financial assistance, emergency shelter and mental health screenings. The center also can help with enrolling children in Montgomery public schools and other needs.

Despite the rising numbers, Prince George's officials said they are prepared to provide housing and assist survivors.

"We are still prepared to help everyone," said John Erzen, a spokesman for Prince George's County Executive Jack B. Johnson (D).

Staff writers Maria Glod and Theola S. Labbe contributed to this report.

Hurricane Katrina evacuees fill out registration forms at a job fair sponsored by the D.C. Department of Employment Services. The number of evacuees in the District was tallied at 380.