The 2000 Census is showing huge increases in the number of same-sex couples sharing households in the District and the nation, reflecting a decade's worth of political and social gains that have made gay men and lesbians far more willing to report their living arrangements.

Census figures to be released today show more than 3,500 same-sex couples living in the city, a 66 percent increase over the figures reported in the 1990 Census. Nearly three-quarters live outside the orbit of Dupont Circle neighborhoods that have long been viewed as the center of gay life in the District.

The numbers also grew significantly in 10 states for which figures have been released: More than 700 percent in Delaware and Nevada; more than 400 percent in Vermont, Indiana, Louisiana and Nebraska; and more than 200 percent in Connecticut, Illinois, Massachusetts and Montana.

The statistics are the most recent from the 2000 Census, adding another component to the complex portrait of a nation that is increasingly diverse racially and socially.

The new information does not cover the entire gay population, but it offers a snapshot of gay men and lesbians who have settled into a shared household. The census shows that they typically live in big cities, coastal towns, state capitals and college communities. Yet they also are settling, if sparsely, in such places as Montana's Prairie County, where the census listed two same-sex couples among its 537 households.

In the District, where the overall population has declined, the statistics underscore the gay population as a significant niche in the capital's economic, political and demographic profile.

The D.C. numbers, researchers say, also reflect a typical pattern in which gay male households are more likely to be in downtown gay areas, and lesbians in suburban neighborhoods.

Experts say the increases reflect more a change in attitude than dramatic growth in the number of gay couples.

"These numbers suggest we are almost capturing the entire population of gay and lesbian households," said Gary Gates, an Urban Institute researcher who specializes in the subject. "It suggests that a much broader cross section has reported themselves to the census, which is a researcher's dream."

The 1990 Census was the first to offer people the option to declare themselves as unmarried partners, not just roommates. The census figures do not include the estimated two-thirds of gay men and lesbians who are not living together as couples.

In 1990, only one-third of gay couples sharing a household reported themselves that way on the census, Gates said, citing comparisons with other surveys. But the 2000 Census numbers so far are close to the figures reflected in other research, he said.

However, M.V. Lee Badgett, an economics professor at the University of Massachusetts who studies the gay population, warned that the count did not capture everyone. In a news release from the Institute for Gay and Lesbian Strategic Studies, Badgett cited a survey of participants in the Millennium March on Washington last year that found that 13 percent of same-sex couples did not use the unmarried-partner designation on the census form.

Census figures show that gay men and lesbians are concentrated in places that are politically tolerant or pleasant to live in. More than half of the same-sex couples in Illinois live in Cook County, which includes Chicago. In Provincetown, Mass., according to census numbers, one in eight households is a gay couple.

Having made inroads in the battle for workplace protections, activists hope that the census will fuel their arguments for legal gains on the home front, on behalf of same-sex marriage, adoption and inheritance rights.

"What these census numbers represent is the family structure and how it applies to gay couples," said David Smith, communications director for the Human Rights Campaign, a national gay rights organization. "I think the next decade is basically the decade of the gay family."

In the District, gay couples are distributed unevenly across the city, concentrated in some communities and invisible in others. Half the city's neighborhoods, especially those east of the Anacostia River, include fewer than 10 same-sex couples, according to the census.

Comparable figures for cities known for their large gay populations, including New York and San Francisco, have not been released yet. But among those for which numbers are out -- including Boston, Chicago and New Orleans -- the District stands out. Of the 15 neighborhoods in these cities with the highest concentrations of gay couples, 10 are in the District. The other five are in gentrified areas near the French Quarter in New Orleans.

In several D.C. neighborhoods in the U Street corridor, Dupont Circle and Capitol Hill, one in 20 households is home to a gay couple.

Gates said gay men are more likely than lesbians to live in pricey areas that offer restaurants, nightlife and bookstores because they can afford to do so, since the vast majority are two-earner couples without children. The more suburban patterns of lesbian couples, he said, probably reflect concerns about crime, the greater likelihood that they have children and women's lower earning power.

Paul Kuntzler, a gay rights activist who lives in Southwest Washington, sees the census figures as confirmation that his community no longer stands apart, something he said he and his partner never dreamed of when they met in the early 1960s.

Locally, anyway, "we don't seem to stir much conflict," said Kuntzler, 59. "There's less segregation, more assimilation, general acceptance, a feeling among gay people that they don't have to be in a totally gay situation to feel comfortable."

Dan Hawes, 29, a field organizer for the National Gay and Lesbian Task Force, sees the numbers as a political weapon. As he and his partner filled out the census form in their Adams Morgan condominium, he said, they saw themselves included in "federally sanctioned statistics."

"It recognizes that we are a constituency," Hawes said, "just like other groups are."

Director of computer-assisted reporting Ira Chinoy and database editor Dan Keating contributed to this report.