The federal government has opened the doors of public housing to unmarried couples living together and to homosexual couples.

All they have to do, if they meet public housing income limitations, is show a "stable family relationship."

The new policy is subject to approval of local housing authorities.

The action was taken by the Department of Housing and Urban Development under a new package of public housing regulations, which quietly became effective May 9.

Priscilla Banks, the HUD housing program specialist who wrote the new rules expanding the government's definition of the family, expressed surprised that there was so little public outcry when the regulations were first published and the government sought comment.

Public housing aid has traditionally gone to low-income, married and heterosexual couples with families, to single-parent families or to those with a common-law relationship that met state tests.

The expanded concept of the family is "very brand new" and liberalizes the country's housing policy, according to Banks, who said she wrote the rule to eliminate discrimination against unmarried persons who live together.

Banks said the new rule of eligibility will cover men and women who don't get married, or homosexual men and women, as long as they have pooled their resources and have lived together for a long time. "Why exclude those persons?" she said.

Approximately 13 million adult men and women lived together as unmarried heterosexual couples in 1976, according to the Census Bureau. The number doubled from 1970, when 654,000 unmarried men and women shared households.

Banks said she had to fight for the new rule within the department, and she was surprised that it took effect with little public reaction.

"I kind of held my breath, and I didn't really expect it would go through. I don't know whether it stuck through or what," she said.

She said the rule was needed because people were complaining that they'd been denied assistance because they didn't fit the departments concept of family as group tied by marriage, blood or common law.

"These people were being discriminated against, for no reason," she said.

Under the new regulation, a family consits of "two or more persons, sharing residency whose income and resources are available to meet the family's needs and who are neither related by blood, marriage, or operation of law, or have evidenced a stable family relationship."

One of the 2,800 local public housing authorities or the private housing owner who rents to a subsidized family under "Section 8" of the federal housing program will determine in each case what is a "stable family relationship."

Banks said, "we're hoping that the PHAS (public housing authorities") out there are liberal enough to interpret it generously." An applicant who is denied eligibility may appeal the local decision to the department, she said.

The department got very little response to its new concept of the family, which covers family units among 1.5 million public housing apartments and 333,000 private housing units for which the federal government may pay rental subsidies in fiscal 1977.

Out of 49 letters commenting on the Dec. 16 recommendations, only six mentioned the new definition of the family.

Two correspondents thought the family definition was unclear, two approved of it, and the final two disliked it.

Joseph F. Laden, executive director of the Albany Housing Authority, thought HUD should specifically exclude from its definition of the family two adults of the same sex.

Robert I. Shirer, of Shirer and Associates, Inc., which manages housing projects in St. Petersburg, Fla., explained his displeasure on March 18, two months after the official comment period ended.

He said the ambiguity and permissiveness of the definition would cause legal disputes, undermine the stability of the community and make it difficult to collect proper rents, because family income and membership would change frequently.

"Does a month or six months constitute a stable relationship? Does the word of the resident suffice?" Shirer wrote.