Almost 50,000 poor families in the Washington area are on waiting lists for rent subsidies or public housing, local officials say, waiting up to seven years in homeless shelters, run-down apartments or homes they can't afford.

In the worst cases, the people waiting "aren't eating as much as they should or they are living on the verge of eviction," said Philip "Knox" Hayes, policy chief for the D.C. Department of Housing and Community Development.

Many struggle to pay more rent than their incomes can support, housing officials in the District, the Maryland suburbs and Northern Virginia say. Others wait temporarily in shelters or share crowded apartments with two or three other families. All are waiting for a better life in a region where rents and housing prices rose relentlessly for a decade.

The waiting is hard for people such as Barbara Gray, of Alexandria. She takes home $800 a month and her apartment rent is $540.

The 23-year-old single mother alternates paying her bills; some will get paid this month, others will have to wait till next month. Utility cutoff notices are part of the routine.

"I have sat and just cried about my debts," said Gray, a teacher's aide. "I work hard every day and still just barely can make it."

The number waiting across the region has increased by more than 15,000 since 1985. In the District, which has 19,000 households on its waiting list, the average wait is seven years.

The bulging waiting lists reflect a growing need for affordable housing, say officials throughout the region. More than 146,000 households in metropolitan Washington need some kind of help obtaining adequate housing, according to the Metropolitan Washington Council of Governments.

But even as budget cuts have made federal programs and local agencies less able to fill that need, the area lost 78,000 housing units that were affordable for low- and moderate-income families from 1980 to 1985. Many were replaced with housing for the more affluent.

Gray would like to get on the waiting list for a rent subsidy. But the city isn't taking any new applicants, and even if it were, 782 Alexandria households are waiting ahead of her.

"I don't understand why it is so high in this area," Gray said. "Here you can't find anything {to rent} under $500 . . . . This is just crazy."

Taken together with the stories of families struggling to get by, statistics portray the growing spread between what some area residents earn -- particularly in service jobs -- and what it costs to live here.

According to a private statistical service, Donnelley Demographics, about 25 percent of the region's households grossed $24,999 or less in 1989.

Cashiers, sales clerks, janitors and local government workers are trying to get by in an area where the average two-bedroom apartment rented for $729 last year and where the median price for a single-family house stood at $191,985 in April.

"Personal incomes have not kept pace with the rise in costs for rental units and for-sale units," said Peggy Sand, housing planner for the Council of Governments. "There are working people that have become homeless, and it's a tragedy."

After three months in Carpenter's Shelter for the homeless in Alexandria, Marcus and Sharon Parks finally saved enough money to move into a two-bedroom apartment with their 3-year-old son. But they wonder whether they can keep up with rent of $640 a month on a combined gross income of $17,000.

Sharon Parks, a city employee, said she and her husband, a landscaper at Georgetown University, have spent a lot of time lately worrying about how to pay the rent and the electric bill while still affording food and gasoline.

"You think, 'How I am going to do this?' . . . . It's almost impossible," she said. Her husband is looking for a second job, she said, adding that her family probably would apply for subsidized housing if it were available.

"Now I understand why a lot of people want to leave the area: the cost of living," Parks said.

Regional officials are concerned that the lack of affordable housing for families such as the Parkses could hurt the local economy. The Council of Governments is scheduled to release a report in September that encourages employers to provide housing assistance to workers.

According to the council, many of the 1.4 million jobs that will be created locally from 1995 to 2010 are likely to be for service workers.

Alexandria City Manager Vola Lawson said "affordable housing is the most important issue that we face." More than 60 percent of city workers live outside the city because cheaper housing is available in neighboring communities, Lawson said.

From 1980 to 1989 in Alexandria, the average rent for a two-bedroom apartment jumped 119 percent to $778, while the average assessed value of a single-family house increased 120 percent to $204,000, housing records show. During the same period, median household income in Alexandria rose by 88 percent to $40,265.

Federal officials say households typically should pay no more than 30 percent of their income for housing. To afford that average $778 two-bedroom apartment, the required annual income would be more than $29,000. But 29 percent of Alexandria's households last year earned less than that amount.

These financial facts of life have forced thousands of area residents to seek help with housing. Faced with a growing number of applicants that it could not serve, the Alexandria Redevelopment and Housing Authority closed its waiting list in 1982 and has opened it only three times since.

"We came to the conclusion that it was inhumane to tell people that we'd take their application and then politely tell them that they might be waiting seven years," said Ken Monn, assistant to the director.

Angus Olson, the agency's executive director, said his office has turned away 560 people since December, the last time the list was open. Almost 700 households applied during the two weeks the list was open then. Fairfax County opened its waiting list July 2 and had 436 applicants in nine days.

Families search for subsidized housing because of the potential savings. In many cases, residents who receive federal assistance pay no more than 30 percent of their income for housing. In Alexandria, public housing residents on average pay between $130 and $350 a month.

Advocacy groups say the federal government should step in more boldly to fill the housing gap. Barry Zigas, president of the National Coalition for Low Income Housing, blames cuts in federal Housing and Urban Development programs under President Reagan.

The poor "have found that they have run out of options," Zigas said. "There is no safety net."

I. Toni Thomas, manager of HUD's Washington field office, agreed that demand for public housing and rent subsidies is increasing, but disputed that the federal government is doing less to meet the demand. "We have maintained our commitment," Thomas said.

Trying to pin the blame on the federal government opens a numbers game. Construction of public housing units nationwide dropped from 51,500 in 1981 to 9,500 in 1987, but the number of people living in subsidized housing grew from 2.4 million to 4.3 million, mostly because more people were given rent subsidies to live in privately owned housing.

Critics point out that the number of new families served each year dropped from 316,000 from 1977 to 1980, to 82,000 from 1981 to 1989.

But while the issue is being studied and debated, people such as Barbara Gray keep wrestling with rent they can't afford -- until they give up.

She soon will be forced to share her home with a roommate to split the rent, or she will have to leave Alexandria.

"I'm just living paycheck to paycheck," she said.