Third grader Lisa Myles, 8, is ''scared'' about the prospect of leaving behind Berwyn Heights Elementary to ride a strange school bus to Spring Hill Lake Elementary next week.

She worries that perhaps "they bus drivers forget you," or "I'll forget the bus number." Berwyn Heights was closed permanently last June.

With the wisdom of an 11-year-old, Thad Jacobs summarized the reasons he is leaving Prince George's County public classrooms to attend parochial schools.

"When I was in the first grade, I had to leave College Park Elementary School , and this year I had to leave Berwyn Heights. . . . It's dumb changing schools, going back and forth," he said.

Patrick McCusker, 11, a former classmate of Thad's who will enter the sixth grade at Spring Hill Lake in September, said: "I'd rather be going to my own school Berwyn Heights ."

Lisa, Thad and Patrick are among 6,621 Prince George's public school students who are affected by last June's closing of 22 elementary and junior high schools. By 1985 an additional 22 schools will be closed, bringing to a total of 65 the number of county schools shut down since 1977.

The school board voted in late February to close the 22 schools, including Berwyn Heights, because of the need to eliminate an estimated 31,000 pupil seats that would otherwise be empty by 1985.

The projected decline in students from a peak of 162,000 in 1972 to 116,000 this fall -- a 28 percent decrease -- reflects a national trend. Locally, it parallels the enrollment drop in Montgomery County, where the decrease over the same period is expected to be 25 percent, from 126,000 to 95,000.

Linda Sinclair, a Berwyn Heights parent, said "absolutely not" when asked if the school board had made the right decision in closing the local school.

Diana McCusker, former Berwyn Heights PTA president and current head of the Prince George's County Council of PTAs, said, "Spring Hill Lake (where the neighborhood children will go) is very large, and they're used to a small, friendly neighborhood school. Now they're going to one of the largest schools in the county."

"The students' education is going to suffer," said her husband John. "We're talking about the basics, the reading and the math, and the extras like art and music, because there won't be the facilities for volunteers" to come into the school to help teachers.

The loss of a neighborhood school in Berwyn Heights, where one has existed for 96 years, represents more than the closing of a small elementary school, distressed parents said.

The school "was the center of the community," said Robert Garofalo, the parent of a fourth grader and a sixth grader.

Elections were held in the school, and the town recreation council used the building for a variety of events.

Planners of the annual Halloween party are already bemoaning the fact that Berwyn Heights doesn't "have another space that large," Ann Garofalo said.

Parents of Berwyn Heights students are preparing to cope with the change in several ways.

Ethel and Michael Jacobs, Thad's parents, have decided to enroll their three grammar-school-age children in parochial schools.

"We're going to a private system rather than putting up with the public school system," said Ethel Jacobs.

"We're going with Spring Hill Lake," said Grace Myles, Lisa's mother. "Financially, we can't afford to put our kids in private schools. They're going to have to ride a school bus, which they're a little frightened of, but I guess it's a new thing they're going to have to put up with."

She said her children "probably will have to take the bus from a sitter's house in the morning and return home on a different bus in the evening."

Martha Longbreake said she and her husband William are trying to make the transition from Berwyn Heights to Spring Hill Lake this fall an "adventure" for their kindergartner and second grader.

"My kindergartner can't wait to ride the bus to school," she said.