Four of the nation's 10 richest communities are in the Washington metropolitan area, according to new census figures released yesterday, but Fairfax County lost its coveted No. 1 status to a surging suburb of Denver that was frontier country only a few decades ago.

Montgomery County, which had been one of the top 10 wealthiest counties in the nation for at least two decades, fell to 13th place.

Among the nation's largest metropolitan areas, the Washington region held its high rank on wealth, education and long commutes, and its poverty rate was one of the lowest.

According to the new figures, which come from the census long form that went to one in six households, the Washington area ranks fifth in median household income nationally, slipping from fourth since 1990. It was surpassed by San Francisco's climb from 10th place, pushed by the dot-com economy that was booming when the census was taken two years ago but has since crumpled.

The Washington region's median household income is $62,216, which means half the households make less and half have more. (The number differs from figures in the Washington Post last week that were based on another definition of the region. In order to make comparisons, today's story uses the official Census Bureau region, which stretches from West Virginia to suburban Maryland, excluding Howard and Anne Arundel counties.)

Among the nation's richest communities, based on median household income, are Fairfax County, which ranked second, Loudoun County at third and Howard County at 10th. Falls Church, which the Census Bureau considers a county, ranked eighth. Loudoun zoomed up from 11th place.

Among counties with a majority black population, Prince George's was No. 1, with median income of $55,256, even though its household income figure declined in the 1990s after being adjusted for inflation.

The bragging rights for richest county go to Douglas, Colo., a 176,000-person bedroom community between Denver and Colorado Springs. It was the nation's fastest-growing county in the 1990s, nearly tripling in size.

As recently as 1950, Douglas County was so sparsely settled that it fit the official definition of frontier, with fewer than six people per square mile, according to Robert E. Lang, director of the Metropolitan Institute at Virginia Tech.

Douglas and other small communities can change far more quickly than large ones, such as Fairfax, said regional economist Stephen Fuller, who teaches at George Mason University.

Lang, too, agreed thatit is better to benchmark Fairfax against other large counties with an employment base that draws a growing number of low-income immigrants.

"I cannot believe that Fairfax hung in that long [in the income top ranks], given that it's almost a million people and that it's so diverse and complicated," Lang said.

Although the region's poverty grew during the 1990s and may have grown since the census was taken, the Washington area had a poverty rate in 2000 of 7 percent, ranking 99th of the 103 metropolitan areas with populations of at least 500,000.

It ranked 30th in the proportion of homes considered severely crowded, meaning they had more than 1 1/2 people per room.

And despite fears of high housing costs, the region dropped in the rankings of people paying more than a third of their income in mortgage or rent. Fuller said that may be because newcomers had incomes high enough to afford the region's relatively high housing costs.

At the same time, 18 percent of the region's homes had at least nine rooms, surpassed only by Salt Lake City. "They actually have kids in those rooms," joked Lang, contrasting the big families of Utah with Washington's smaller ones. "We have hobbies in those rooms."

The region moved to first place, passing the university area of Ann Arbor, Mich., in the share of adults with a graduate degree: 17 percent here hold more than a bachelor's. The slog to work is longer in Washington than in any other metropolitan area but New York City and two of its satellite metro areas in suburban New Jersey and Long Island, according to the census data. The average commute in the Washington region takes nearly 33 minutes, compared with nearly 39 minutes in New York, where the heavy use of transit lengthens the journey.

As the Washington region grew, more people drove alone to work and fewer carpooled. As a result, the region, which had been known for its slug lines and HOV lanes, fell from eighth to 24th place over the decade in the proportion of commuters who carpool. Carpooling is now more common in Phoenix, Dallas and Atlanta than it is locally.

The region maintained its status as one of the country's premier destinations for immigrants: It ranked sixth for the total number of immigrants, and seventh for the number of immigrants who arrived in this country during the 1990s.

Audrey Singer, a visiting fellow at the Brookings Institution who studies immigration, said Washington is one of the most prominent "emerging gateways" for foreign newcomers -- among them metro areas such as Dallas, Atlanta and Portland, Ore., that are joining New York, Los Angeles and other historical destinations.