Friends, straight or gay couples, cohabitating seniors and others could walk into the City-County Building, show evidence of their "mutual commitment," and come away with official recognition of their relationship under a proposal introduced by Pittsburgh Councilman Bruce Kraus yesterday.

The proposed "domestic registry" would allow certain city employees to share their fringe benefits with partners, and other employers could opt to treat registrants like married couples. More broadly, it would allow almost any two city residents to "legitimize their relationships and families," as Mr. Kraus put it.

City Council President Doug Shields called domestic registration "another phase in the development of enfranchising people in this country."

It's unclear whether opponents will emerge to try to stop the proposal.

Loni McCartney, of Carrick, said she would register even though her private employer wouldn't let her lesbian partner share her benefits.

"It's not a marriage. It's not going to give me any other rights that [gays] are fighting for," she said. But it is "a way for the city to recognize my relationship."

Mr. Kraus said Philadelphia, Salt Lake City, Seattle and Urbana, Ill., are among the cities that have domestic registry.

"It makes us a much more desirable location for young, bright, cutting-edge people who want to come in and live in progressive areas," said Mr. Kraus, who is openly gay. "It really is about being a good place to attract progressive employees and employers, and grow."

Under the legislation, any two unmarried city residents -- unless they are related too closely to be married under state law -- could apply with the city Personnel Department. They would have to show three pieces of documentation of "mutual responsibility," which can include loan papers, utility bills, insurance policies, wills, powers of attorney, contracts, motor vehicle titles, bank or credit account statements, or evidence of shared child care responsibility.

They then would pay $25 to be certified in the "mutual commitment registry." The designation would apply until one party either presented an affidavit ending the relationship or died.

City employees have long been able to extend their benefits to partners other than a husband or wife, and the legislation would better define that process and modestly extend it, said Mr. Kraus.

The Personnel Department did not respond yesterday to a request for the number of city employees with domestic partner benefits.

In Seattle, which has had a registry since 1994, there are 3,677 registered pairs. Around 2.4 percent of the people covered under the city's insurance are registered domestic partners. Domestic partners and their children amount to 1.5 percent to 2 percent of insurance costs, according to the mayor's office in that city.

In Urbana, on whose 2005 law Mr. Kraus' proposal is based, only four city employees are among the 94 domestically registered couples. The biggest employers in that city of 38,000 accept registry as a criteria for providing joint benefits, said Urbana City Clerk Phyllis Clark.

There were no legal or legislative challenges to Urbana's law, she said.

Salt Lake City's experience, though, shows how controversial a registry can be. New Mayor Ralph Becker made domestic registry a top priority and got it passed unanimously by council, then had to fend off an effort by state legislators to preempt the law. It survived, and 19 couples have registered since May.

The Alliance Defense Fund, a conservative Christian nonprofit organization, sometimes challenges local laws it deems to be steps toward "same-sex marriage." The fund, which has sued Pittsburgh over legislation restricting abortion protesters, did not respond yesterday to questions about whether it would become involved in the domestic registry debate.

Mr. Shields is co-sponsoring the legislation, which seems to have some early support, tempered by questions about its impact.

"I don't have a problem with it," said Councilman Jim Motznik. "I think people should be treated the same, regardless of religion, or sexual orientation" or other characteristics.

"I do believe family is a broad and inclusive term," said Councilman Ricky Burgess. Marriage, though, is between a man and a woman, said Mr. Burgess, who is a church pastor.

"I will not support any legislation that alters that definition of marriage," he said, but he hasn't determined whether this proposal would do that.

Discussion and a tentative vote could occur as early as next Wednesday, but council could postpone that pending a public hearing.