If it weren't for the daily "lunch and fun" nutrition program near her home, 71-year-old Matilda Schuster shyly told an audience of senior citizens yesterday that she would usually not have anyone to talk to. "I get very depressed sitting at home," she said.

The plight Schuster described is hardly unusual in Montgomery County, where a new survey of the county's 71,450 noninstitutionalized senior citizens lists isolation as "the most crucial problem facing the elderly."

According to the study, the edlerly population in the county is increasing at 3 1/2 times the rate of the county's general population growth.

"Social isolation is the key element which contributes to physical and mental degeneration in older people, thus costing them their independence," said Sally Forden, producer of "Generations Together." Generations Together is a radio program produced by the county's Commission on the Aging.

Speaking at a hearing on the county's "Area Plan for Programs on the Aging" yesterday, Forden said, "The people who talk with me on the radio (are concerned about) how best to support and encourage the need for continued independence in old age and at the same time combat social isolation."

Until recently, the elderly population in Montgomery has been a relatively hidden minority. Yet statistics resulting from surveys identify them and their needs and produce a detailed and sometimes astonishing composite of the county's elderly population.

Although they are well educated - more than half have high school diplomas and 14 percent hold advanced college degrees - 57 percent reported they are "not looking forward to doing anything next week," 39 percent said they were "not particularly excited or interested in anything in recent weeks" and 29 percent "hardly ever visited with their neighbors."

A total of 27 percent live alone, and of this number, just under half are 75 years old or olders.

While many are "independent and self-sufficient," more than 2,000 are in "almost desperate need of assistance" of various kinds and another 20,000 have problems they are unable to resolve by themselves.

According to the study and their testimonies, the major problems Montgomery County senior citizens face include insufficient income, lack of adequate transportation to the programs available to them, fear of crime, poor health and nutrition and shortage of affordable housing.

For example, although the county has a lower than average ratio of physicians to population, only some doctors will accept Medicare and Medicaid payments and an insufficient number specialize in geriatric problems. "For the first time this year the county health department has come forward and said we now recognize there are senior citizens and not only children and pregnant mothers," testified Rodney Crowther, 82, of the Commission on Aging.

The high cost of drugs is a particular concern, and often takes what remaining cash older people have to spend after they pay for housing, utilities and food.

About 10 percent have incomes under $3,000 annually and live alone, yet only 1.2 percent receive food stamp assistance. The report attributes this deficit to the complexities of applying for assistance and a reticence among senior citizens to admit to the need.

While slightly more than two-thirds own their homes, those under the median over-65 family income of $20,544 have difficulty keeping pace with rising assessments and utility rates. The median income for elderly heads of households is 23 percent below the county average.

"Elders tend to reduce their expenditures on food and medical care to avoid losing their home," the report stated.