NEW YORK – With strong backing from the Census Bureau, gay-rights activists are urging maximum participation by their community in the first U.S. census that will tally same-sex couples who say they’re married — even those without a marriage license.

The move has drawn fire from conservatives, who complain that it’s another step toward redefining marriage.

For the first time, the bureau has deployed a team of professional field workers — about two dozen strong — to reach out to gays and lesbians. On Monday, the bureau unveiled its first public service videos asking gay Americans to mail in their census forms.

“What I tell folks in the bureau is that this is a powerful, important part of American society,” said Tim Olson, a Census Bureau assistant division chief helping to oversee the campaign.

“We have to reach out and engage this part of the population. Anything less than that is a failure,” he said.

Only the District of Columbia and five states — Massachusetts, Connecticut, New Hampshire, Vermont and Iowa — have legalized gay marriages, starting with Massachusetts in 2004. But the Census Bureau says same-sex couples in any state who consider themselves spouses should feel free to check the “husband” or “wife” boxes on the census form, rather than “unmarried partner.”

The bureau’s willingness to count gay marriages — despite a federal law that denies legal recognition to any of them — has been hailed as a historic milestone by gay-rights leaders.

“It’s humongous,” said Jaime Grant, director of the National Gay and Lesbian Task Force’s Policy Institute.

Some conservatives have complained that the eventual count of same-sex unions will be legally inaccurate while serving as ammunition for gay-marriage advocates.

Gary Randall, president of the Bellevue, Wash.-based Faith and Freedom Network, complained in a blog posting last month that the census “is leaving it to responders to characterize their own relationships, regardless of legal status.”

“Will homosexual numbers be inflated by this ‘you decide what you are’ policy? Probably,” Randall wrote. “This policy shift is another attempt to confuse the discussion about marriage by creating a problem of sorts, then providing a solution that advances the homosexual agenda of redefining marriage.”

Olson said he was aware of the criticisms, but defended the Census Bureau’s policy of counting people according to how they identify themselves.

“We’re treating the gay community the same as other segments of the population,” he said. “There’s a respect factor there. … We’ve never asked people to show us their marriage licenses. We don’t do that for straight people.”

Olson also stressed the confidentiality of the census — insisting, for example, that gay members of the military should have no fear about identifying themselves as part of a same-sex union, even though the “don’t ask, don’t tell” policy forbids gay service members from being open about their sexual orientation.