The large number of kindergarten pupils in Washington area schools this year has significantly helped reverse a decade of declining enrollments in some school districts and slowed the pace of the decline in others, according to September enrollment figures released yesterday.

The September enrollment counts from four of the area's six school districts show that dramatic increases in the number of children in the lower grades is making up for a continued decline of students in upper grades, school officials said.

Preliminary figures gathered at the end of the first week of school suggested the upturn. Officials said the Sept. 28 count, considered a reliable indicator of enrollment for the year, shows an end to the massive decline in student population that forced hundreds of school closings in the past decade.

Montgomery County reported the largest enrollment gain over last year's figures, with the enrollment now at 91,670. According to Ken Muir, a spokesman for the school district, there was a net gain of 606 students this year, which overshot the district's projections by 795. It is the first time since 1972 that enrollment has grown, said Muir.

Much of the increase came from a gain of 695 kindergarten pupils and 613 second graders this year, he said, but it was countered by a loss of about 600 seventh graders and about 450 10th graders.

Muir said the increase in enrollment was due to higher birth rates and an increase in housing construction, especially in northern Montgomery County. "We were projecting a turnaround, but it has come a little sooner than we expected" because of the pace of building, he said.

"It's the first time we have been hiring rather than reducing the number of elementary school teachers," said Muir. The availability of qualified teachers "might get tighter before the college enrollments in education programs pick up."

The Arlington school system reported a net gain of 289 students. The largest increase was in the first-grade class, which picked up 143 students over last year. In all, 14,643 students were enrolled as of Sept. 28.

In the District, as of Sept. 13, the number of pre-kindergarten students was up 109 and the number in kindergarten grew by 313. Although the District had a net loss of 979 students, the pace of the decline has slowed, said Cormac Long of the Division of Quality Assurance, the office that evaluates school programs. The total number of students attending District public schools this year is 86,168, he said.

"I think for the first time we were underestimating our enrollment," Long said. Five years ago the district lost 5,000 students in one year.

In Prince George's County the decline in the number of students from last year was not as great as had been expected. Although the school system lost 2,310 students, 334 more than expected enrolled, 24 of those in kindergarten classes.

Prince George's county public schools enrolled 105,886 students in all this year, compared to 108,196 last year. "The elementary pace of the decline is slowing. We have more kindergarteners this year than last," said John Peterson, a school system demographer. We "finally turned the corner, but its nothing like the baby boom."

September enrollment figures were not available for the Alexandria and Fairfax public school systems.