The 45-year-old woman looks forward to a picnic soon with her son, two daughters and a social worker. It's been more than a year since she has seen her girls and at least four years since she last saw her boy.

The woman, Charlotte, is retarded and unable to care for her children, who have lived with an Upper Marlboro foster family since 1976. "I miss them. I haven't seen them for so long, it ain't funny," said Charlotte, whose last name is being withheld at the request of social workers.

But her children are happy and Charlotte says she doesn't mind that her daughters, aged 15 and 12, will be adopted by their foster parents. She knows the family well. It is one of four foster homes, three of them in Prince George's, in which she herself has lived during the past seven years since she separated from her husband, an alcoholic, with whom she and the children lived in Seat Pleasant.

The foster care program has been a blessing for Charlotte and her family, and is becoming a refuge for an increasing number of children in Prince George's.

Social workers insist foster care is a last resort, used only when other measures to keep a family together fail or when a child is in danger of harm at home. But during the first five months of this year, the number of children in foster care in the county increased by 10 percent over the first five months of 1981, in part as a result of family stress caused by unemployment or other economic problems.

Through May, 118 children were directed to foster care by the courts, which make the final decision in each case. For 36 of the children so far this year, it was at least the second foster home. In all, about 700 children currently reside in Prince George's foster homes. In Maryland, Prince George's ranks second only to Baltimore County, which has 4,200 foster children, in the number receiving care.

But the problems in Prince George's go beyond the growing caseload.

Seventeen out of about 40 staff positions in the division of adoptions and foster care were lost this year because of funding cuts in federal programs such as Title XX, which supplements state money used to pay for county social services. Although the cuts have hurt the division, foster home-finding supervisor Carol Siemens hopes four new full-time and two contract positions recently authorized by the state will ease the workload. Throughout the department, social services lost a total of 47 employes.

In contrast, Montgomery County has 12 1/2 fewer staff positions in its Social Services Department. Five of the cuts were in the 27-member foster care division, but the state has provided money to reinstate three positions, according to Mary Lou Hurney, chief of child welfare. The division, she said, should have little difficulty handling its foster care caseload, which totals 682 and has decreased somewhat since January.

Ironically, while fewer Prince George's workers struggle to care for more foster children, the county faces the prospect of losing still more federal money if it cannot reverse the trend and cut its caseload. Nell Vincent, director of Prince George's adoptions and foster care division, said all the states were instructed this year by the federal Department of Health and Human Services to reduce their foster care caseloads by 30 percent in stages over the next four years.

This may become an unusually difficult task unless the economic climate improves. Vincent said Prince George's workers are seeing more cases of severe child abuse and neglect which can be traced to the deterioration of the economy.

Parental stress triggered by prolonged unemployment or the pressure of unpaid rent and bills can lead to hostile behavior toward a child, she explained, adding, "If you have a job, you're not as prone to beat your child. When a situation becomes stressful, that's when the family breaks down."

In Prince George's, 1,185 fewer families received welfare checks this fiscal year through the federal Aid to Families With Dependent Children program (AFDC). Last year, AFDC payments went to 8,300 families. In the same period, the number of food stamps recipients dropped from 13,000 to 11,000.

Families evicted from their homes also look to foster care as the resolution, at least for the short term. Referring to the weekly calls he gets from parents hoping to place their children in foster homes, Phil Newsom, supervisor of emergency shelter services, said:

"They see no resolution to the problem. They can't afford an apartment. They've exhausted their resources. . . . They've hit bottom and feel they are failures. They see foster care as the way to keep kids from suffering the consequences of being in the streets."

But a shortage of case workers, funds and foster parents frequently prevents foster care workers from handling such cases, which may not qualify as emergencies.

In addition, the emphasis in foster care has shifted to establishing a permanent plan for children when they leave home, rather than providing a temporary respite from parenting for overburdened adults.

"We try to keep children out of foster care. Once a family has broken up it's hard to get them back together," said Paula Horowitz, director of intake services, which refers community inquiries to the appropriate social services divisions, including foster care.

Day care, homemakers' services and adult counseling are seen as measures that can improve home situations and keep children out of foster care. But in the past year, funds for these services have also been cut.

When these attempts fail and children must go into foster care, they go to homes like that of Ann Fenner, who became a licensed foster mother in 1979 and receives a stipend of just over $200 per month for each child. Five months ago she and her husband, a Greyhound bus driver, welcomed two sisters, Ebony, 8, and Erin, 13.

The girls fit right in with her two sons, aged 3 and 7, Fenner said. "It couldn't be better," remarked the District Heights resident, adding, "The second day they wanted to call me 'Mommy.' "

"To me, it was like a challenge," said Fenner, explaining why she became a foster parent. "I always wanted girls and I was sure there were some girls out there who needed a home."

Fenner, who is identified here with her maiden name to ensure the privacy of her foster children, is a bank employe. She said she has little difficulty communicating with the girls. "I lay down the rules and they don't have problems dealing with it."

Another foster mother, who is unmarried, said some of her colleagues questioned her decision to become a foster parent. But she said the "shock" of those who doubted her passed when they saw how serious she was about her role as foster parent. The woman has cared for a 13-year-old girl for the past 10 months and recently was granted permission to adopt the teen-ager, whose mother, she said, was emotionally unstable.

Earlier this year, the Maryland General Assembly passed a law allowing children to move more quickly through the foster care system and become eligible for adoption in two years. Previously, a case could be held up in the courts for an interminable period, decreasing the likelihood that a permanent home for the child could be provided.

In 1981, the Prince George's adoptions division placed 63 children in permanent homes.

The law should decrease the average time a child spends in foster care, which is currently 6.2 years in Maryland. Nearly three-quarters are in care for more than two years. The new child welfare act may lower the length of time children are "bounced around" between homes, said Siemens.

Siemens praised the intent of the law, which is to move children out of foster care permanently, either back to their biological parents or to an adoptive home, but said "it doesn't work if you don't have the staff" to work with the families to develop alternative plans. "It's self-defeating."