A chart with yesterday's story on growing elementary school enrollments erroneously reported the projected five-year enrollment increase in eastern Loudoun County. Enrollment there is expected to increase 83 percent. Figures given for eastern Prince William apply to the entire county.

If the students at Newington Forest Elementary School in Springfield lined up for a school photo, the results would be striking: one in every three students would be in kindergarten or first grade.

This year 271 of 747 students at the Fairfax County school are in those classes, and next fall the school expects to reach its capacity of more than 800 students, with much of the increase coming in the first two grades.

At the nearby Little Run Elementary School east of Fairfax City, a surge in kindergarten and first grade enrollment may have saved an older school from being closed or consolidated -- always an emotional community issue.

Both schools -- and scores of others throughout the Washington area -- are benefiting from what educators say is a baby boom that began in the late 1970s and is beginning to fill schoolrooms after years of declining enrollments.

"It's a boomlet," said Prince William County school planner Charles R. Wildman. "It's not going to be as long as our baby boom of the past, but we're keeping our eye on the birthrate."

Educators from Upper Marlboro to Leesburg are predicting that the baby boomlet will force construction of millions of dollars in new classrooms and hiring hundreds of new teachers. Washington's fast-growing outer suburbs, already faced with demands for new schools, are likely to be hit by calls for higher taxes to finance the expanding enrollments.

Susan Carmon Gewirtz, a finance expert with the National Education Association, says the boom, fueled in part by the rise in births to mothers in their 30s, could not have come at a worse time. The Reagan administration's efforts to cut federal spending will mean less aid to school districts, she said. "Thinking about raising local property tax rates and raising state aid and not being able to count on the federal government . . . is going to catch people by surprise," she said.

Educators in the Washington area are not alarmed by the enrollment increase and they generally predict little public resistance to higher school spending. "In Loudoun County, we've always had the support of the citizens on school needs," said Arthur A. Welch, assistant superintendent for planning in a system that will see some of the sharpest increases in the region. "I don't think the citizens here would like to see overcrowded schools and double sessions."

County officials in Fairfax, Montgomery, Loudoun and Prince William, facing a housing boom as well as the baby boom, plan to build at least 19 elementary schools in the next five years and hire hundreds of new teachers. Even in the District, where the boomlet is modest, a number of upper elementary teachers recently were reassigned to teach lower grades.

Some educators voice concern that educational programs will suffer from competition for funds needed to pay the cost of increasing enrollment. "There are not that many dollars," said Louise F. Waynant, an assistant superintendent in Prince George's County. "The first priority will be dealing with the increased number of students."

The birthrate nationally began to climb in 1977, and this year the National Education Association says there are 54,000 more elementary school students in the nation's classrooms, the first noticeable increase in 14 years. The growth will continue into the 1990s, according to the National Center for Education Statistics. It predicts that enrollment in kindergarten through grade eight, now 26.6 million, will reach 30.5 million by 1993.

Even so, many closed schools in the Washington area will likely not need to be reopened, educators say, because young families are moving to areas where there are few classrooms -- such as western Fairfax, the Rockville corridor and Columbia.

Officials also say they were cautious in closing schools when rolls began to drop a decade ago. "There was a lot of pressure on us to close schools," said James P. Akin, Alexandria's acting elementary school director. "There was no rhyme or reason to close them. We took a lot of heat from people for that."

School forecasters predict little or no elementary school growth in the District, Arlington and Alexandria, although some neighborhoods will grow. One reason is that housing in the District and built-up suburbs is too expensive for many young families.

The burgeoning birthrate that is just hitting the schools is likely to have spinoffs, the officials say. More mothers are working, so demand is up for nursery school, prekindergarten classes and school-based day care.

The District added $1.6 million to its budget for prekindergarten classes this year. At Janney Elementary School in upper Northwest, there is a waiting list for prekindergarten classes, which appeal to ambitious parents who want their 4-year-olds to study math and reading skills, science, music and art. Janney, a beneficiary of improved parent confidence in the public schools, also has waiting lists for kindergarten and day care, Principal Emily J. Crandall says.

Other jurisdictions also are feeling pressure from working parents. Fairfax County has 45 classrooms assigned to day care programs. Prince George's plans to open half a dozen "workplace schools" next fall, where busy parents can drop off children at 7 a.m. and pick them up at 6 p.m.

Local officials emphasize that the current "echo baby boom," as demographers call it, will be modest compared with huge birthrates just after World War II that boosted public school enrollment from 29.5 million in 1954 to 46.1 million in 1971. Current enrollment, nearly 39 million, will reach 41.7 million in 1993, according to government predictions.

Still, area educators are planning millions in construction:

* Prince William will open two new elementary schools next fall to handle overflow in the Dumfries and Lake Ridge areas, and two more are tentatively planned for 1989.

* Loudoun plans two elementary schools, an intermediate school and a high school in the next five years. In eastern Loudoun, one of the fastest growing sections in the metropolitan area, elementary enrollment is predicted to soar 80 percent in five years.

* Fairfax County, the largest school system in the region, has a five-year building plan that calls for nine new elementary schools, five elementary additions, a new intermediate school and a new high school. The School Board voted last week to spend $299,000 on 15 portable classrooms to meet crowding problems at various schools.

* Montgomery, which recently closed a number of elementary schools, will build at least six new elementary schools during the next six years, and it is considering building them bigger, with an 800-student capacity compared with the usual 600. The county is looking into reopening a closed elementary school in Burtonsville.

Michael W. Kirst, a Stanford University education professor and former chairman of California's state board of education, has predicted that schools will have to ante up 5 percent after inflation in the next five years -- perhaps 10 percent overall -- just to pay for enrollment increases.

He cites estimates that education improvement efforts proposed by the recent spate of reform reports -- such as higher teacher pay, a longer school year and an upgraded curriculum -- could tack 20 percent onto school budgets.

Prince George's Waynant, a former elementary teacher, said the rising enrollment will boost morale among school employes. "When a school system grows, there is promise, hope," she said. "With more children in school, the public interest is going to be greater. I'm delighted about it."