(San Francisco) The U.S. Census Bureau is making an unprecedented effort to include same-sex couples in next year’s national population count, but legally married gay couples won’t show up as such in the official once-a-decade tally, bureau representatives said Thursday.

Statistical problems related to the development of the 2010 census form and the evolving legal state of same-sex relationships led Census officials to conclude that trying to include married gay couples in the overall snapshot of household marital status could yield an inaccurate number, said Gary Gates, a University of California, Los Angeles demographer who has been advising the bureau on gay issues.

Instead, same-sex married couples will be added into the category for unmarried partners, just as they were for the 2000 census. But in a marked policy departure, the agency plans to make the data on same-sex couples who described themselves as married available on a state-by-state basis.

“The Bureau has decided to give us the information, but be a little cautious,” Gates said.

The decision to develop separate sets of numbers was a compromise position that was “less about politics and more about accurate data,” he said.

Gates stressed that it was important for gay couples to participate in the census, noting that information drawn from the last one had been used in lawsuits dealing with same-sex marriage and to lobby congressional representatives who may wrongly assume they do not have many gay constituents.

Because same-sex marriages were not legal in any U.S. state a decade ago, the 2010 census is the first for which the bureau has wrestled with how to count married same-sex couples. In June, census officials announced that they would make the attempt, reversing an earlier decision made under the Bush administration.

Since then, however, it’s become clearer that a wildly inflated number could be produced if the number of heads of household who said they lived with another adult of the same sex, and described that person as a husband or wife, were only counted.

Some couples in civil unions or domestic partnerships, or who live as spouses in states where gay couples have no spousal rights, have tended in past surveys to identify themselves as husbands or wives anyway, according to Gates.

The annual American Community Survey the bureau produced for 2008, for example, had 150,000 married same-sex couples spread across every U.S. state, even though only two states – Massachusetts and for a 5-month period, California – allowed same-sex marriages. Gates estimates there are probably no more than 35,000 legally married gay couples in the country now.

Undercounting same-sex couples also remains a significant concern, Gates said, since some couples may not be living openly and fear discrimination.

Tim Olsen, assistant chief of the bureau’s field division, told gay community leaders at a census outreach meeting in San Francisco Thursday that the agency is continuing to refine the way it counts same-sex couples and could have the ability to separate married from unmarried couples in time for future surveys.

“We have a big opportunity to create a picture of America that includes us. We are not invisible anymore,” Olsen said.

This census marks the first time that gays and lesbians have been targeted for minority outreach efforts that also include reaching out to groups deemed “hard to reach” because of their disaffection with the government.

The gay community campaign will include a Web site, scheduled to go up in about two weeks, called Our Families Count, as well as advertising campaigns in cities with large gay populations. Among the video vignettes meant to demonstrate the nation’s diversity on the main census site is one featuring a transgender person, Olsen said.

“You will see yourself in these videos, whether you are Hispanic, black, white, mixed-race, gay or straight,” he said.

Although the census has not attempted to count individuals who identify as gay, lesbian or transgender, they could be included in the next count or even future editions of the annual American Community Survey, Olsen said. The survey, which is much more detailed than the 10-question census form that will be mailed to every household in March, is designed to give state and local governments a snapshot of how their populations are changing.

Olsen said gay leaders need to keep advocating if they want to be recognized.

“In terms of 2010, we are set in stone. For 2020, now is the time to start doing what you do best,” he said.