When Prince George's County social workers sent Dianne, Michelle and Charles -- two babies and a toddler -- to foster mother Mary Tyler in 1977, she thought they would stay the usual seven or eight months while waiting to be adopted.

But more than 2 1/2 years later, the three children -- ages 2, 3 and 4 -- are still living with the lady they now call Momma.

"I guess no ones wants them," says Tyler, who has cared for 27 foster children in her Landover home over the last 10 years. "I don't think I've ever had kids to stay this long. There is nothing wrong with them. We just can't find a permanent home for them."

Tyler's foster children are not the only black youngsters for whom the county Department of Social Services has had trouble finding homes.

Over the past year, social workers say, they have encountered increasing difficutly in finding foster homes and adoptive parents for black babies.

As a result, the county has been forced to increase the number of black children staying in foster homes pending adopton, and to increase the number of black children being cared for by white pre-adoptive parents.

"We've never had a problem placing black infants before, except for the last six months to a year," said Diane Banks, a case worker in the Social Services Department's Division of Adoptions and Foster Homes. "We've always had problems finding homes for handicapped children, but never normal black infants."

Each month, the department is given the care of about 20 newborn infants -- half of whom are black -- when their biological parents give them up for adoption.

Since there is a two-year waiting list of prospective adoptive parents for white infants, most of them are adopted immediately. Black babies, however, now must wait an average of eight months to a year while homes are found for them, and there is no waiting list.

Social workers attribute the shortage of pre-adoptive and adoptive homes for black infants to a number of factors. One is the increase in the black population in Prince George's County, which has brought with it an increase in the number of black babies being given up for adoption. Blacks now make up a third of the total populaton in the county.

However, only about a quarter of the potential parents who show up at the monthly meetings held by the social services department are black. Thus, the number of black parents looking for black infants has not increased in proportion to the rise in the number of children available for adoption.

The worsening condition of the economy also is blamed. Observers say black families are harder hit than white ones, thereby making it more difficult for black families to take on the added financial burden of a child.

"A lot of black families get the wrong message," said Tyler, 48."They think that you have to own a big home and a big car, and have oodles of money in the bank. Then, they think about inflation -- and well, you know, blacks don't generally have the best jobs in the world. After a while, a lot of people just give up the idea of taking a pre-adoptive or adoptive child into their house."

She says that while she and her husband are far from well off, monthly payments from the social services department for the children's food, clothes and other supplies make it somewhat easier on them. She also enjoys her work.

"Children keep you young and active," says Tyler, who has raised two children of her own, one now 32, the other 16. "I love children. I feel that God gives us all a vocation, and I think this is one they labeled 'Mary.'"

Percy and Millicnet Warren of Clinton, who have two adopted children, say inflation and unemployment have probably been the chief factors discouraging black families from adopting children.

"It's simply a matter of economics," says Millicent, 32. "While it's true people afford what they want to afford a lot of the time, no parent who cares about a child wants that child to go without the basic necessities."

"We have a lot of friends who have expressed an interest in adopting," says Percy. "The problem is they can't afford it. And that probably won't change until the economy turns around."

Social workers say the dramatic increae in the number of women entering the job market in the last decade has made it difficult to find a parent at home to take care of children.

They believe that this trend has affected black families more because the economic need to have two working adults is greater in black families, who often have lower incomes.

Under social services guidelines, one parent is required to stay at home with a foster infant. Until recently, the same held true for adopting parents. Now, one parents is requird to stay at home with a newly adopted child for only six weeks.

The Department of Social Services has responded to the shortage of black pre-adoptive homes in two ways. In a few cases, black pre-adoptive infants have been placed with white families.

"This has worked out pretty well," says Banks. "We wouldn't usually do that with an older child because that could lead to some real adjustment problems, but infants know no colors."

For the most part, though, the department has opted for placing black infants with black families, like the Tylers, who already have other children awaiting adoption.

"Some people ask me how can I do it (take care of so many children)," said Tyler. "I say, Don't knock it until you've tried it. Once you get into it, it's hard to give it up. Those youngsters just melt right into your heart. The hardest thing is turning them loose when somebody adopts them."

Banks says the Social Services Department has already launched a campaign to get more black families to apply as pre-adoptive and adoptive parents.

"I'll be visiting civic associations, PTAs and various black organizations over the next few months to encourage families to apply," she said. "In addition, we'll be trying to get radio and television time so that we can get our message across. If we can make people aware of the problem. I'm confident we'll get a response."