At age 5, Eric Movshin is already a seasoned student.

It's unlikely there will be a heartbreaking farewell between mother and child when the precocious tyke leaves soon for his first day of kindergarten at Diamond Elementary School in Gaithersburg.

Like many of his peers, Eric has already faced the separation and social adjustments that accompany a child's first school experience. Setting out for school, lunch box in hand, is nothing new for him.

Eric, like many Montgomery County youngsters, has been enrolled in a pre-school program since he was 2, the minimum age for attending school in Maryland.

His mother, Lois Movshin, fears kindergarten might be a letdown, so she's trying to arrange after-school activities to amuse as well as educate her child. It's a frustrating task, she admits, attempting to juggle schedules with a younger child. It's also "extremely expensive," she says, since private school programs such as music or athletics can cost more than $100 a month.

Like many parents in the county, Eric's parents would like to see an all-day kindergarten program.

The Montgomery County Board of Education, under pressure from parents, is studying a plan to convert the county's 268 kindergartens to full-day sessions beginning next fall. The annual cost would be $1.9 million.

The plan includes two alternative budgets for converting schools gradually over two to three years, to keep costs as low as possible.

Since the state does not contribute to kindergarten eduation, the county must fund the project. School Superintendent Edward Andrews and school board member Marian Greenblatt agree that cost could be a major stumbling block in the plan to extend the kindergarten school day.

Greenblatt has recommended that the board ask the state legislature to consider funding an all-day kindergarten program, since she doubts the County Council would be willing to "make such a big commitment as a $2 million annual add-on to the school budget."

What many county educators do agree on, however, is the need for an extended kindergarten program.

The 5-year-olds of today, even those without previous school experience, are more sophisticated than their counterparts of a decade ago, explains Delpha B. Keys, coordinator of early childhood programs for the county school system and author of the all-day kindergarten proposal.

She credits television programs such as Sesame Street, and the more educated parents who encourage their children to develop basic skills.

"The parents are armed with newer information showing infants and pre-schoolers have a tremendous capacity for learning," she said. "They want us to update our kindergartens.

"It's cost-effective to invest in children at a young age. It makes such a big difference. We can change their language and mental development in the formative years and their entire attitude toward learning can be altered. It's 10 times more expensive to do that in remedial work in later years."

The increased cost of living, which often requires both parents to work, and the rise of one-parent families also are factors in the call for an all-day kindergarten program, Keys and Andrews agree. But they both quickly point out the county "is not assuming the rule of the day-care provider."

The all-day kindergarten program Keys envisions would be a "slowed down" version of the present 2 1/2-hour school day. It would combine academics and play, and encourage the development of reading and writing skills.

The biggest advantage of an extended kindergarten program, Kees says, would be the more personal education a youngster could receive. Teachers now handle two kindergarten sessions daily, sometimes with up to 35 children in each.

She said a rest period would be provided for those children who required it. Early dismissal would be permitted for children whose parents felt they weren't ready for an extended program.

Six schools, all in the Silver Spring area, already offer all-day kindergarten sessions. They are Rosemary Hills, Montgomery Knolls, Rock Creek Forest, New Hampshire Estates, East Silver Spring and Woodlin Elementary.

At one of the schools, where the principal assumed that young children would require a nap, 60 cots were oredered. All but one has been returned, since they weren't being used.

Key contends that the 2 1/2-hour kindergarten program is more fatiguing, since there is so much to be covered in such a short time. Studies have shown, Keys said, that "a longer, more restful schedule is beneficial. There's more time for conversation between the teacher and child."