Charter school enrollment in the District, which made up a scant 5 percent of the total public school population in 1998, has broken the 40 percent mark, according to preliminary figures released Monday.

The unaudited data, based on an Oct. 5 count, show charter enrollment at 32,009, an 8.2 percent boost over last fall’s 29,557. Traditional public school enrollment, which ticked up last fall for the first time in four decades, dipped slightly to 46,191, down less than 1 percent (419 students) from last October.

The numbers have been turned over to outside auditors retained by the Office of the State Superintendent of Education to be verified for residency and other requirements. Final figures are expected early next year.

If the trends hold, it means that the “market share” for traditional public schools will for the first time be less than 60 percent. The data also affirm the continued robust growth of the charter sector, which served fewer than 3,600 students in the 1998-99 academic year. There are now 53 charter schools on 98 campuses.

“We’re delighted to see the continued, steady growth in charter school enrollment in the District,” Brian W. Jones, chairman of the D.C. Public Charter School Board, said in a statement.

Fred Lewis, a spokesman for D.C. Public Schools, said nearly all of the enrollment decline in the traditional system was at four schools that encountered what he called “bad press” in the 2010-11 academic year: Dunbar High School, Hardy Middle School, Noyes Education Campus and Thomson Elementary. Dunbar’s New York-based management group, Friends of Bedford, was dismissed by Chancellor Kaya Henderson last December for poor performance. Hardy was roiled by changes in the principal’s office and Noyes by allegations of cheating by teachers and staff on the DC CAS tests. Thomson made headlines when some students were sickened by a classmate who brought cocaine to class.

Mayor Vincent C. Gray chose to celebrate the overall growth of the city’s public schools, which have seen three years of increases on the strength of charters’ expansion. Total enrollment is up 2.7 percent over October 2010, to 78,200.

“These numbers represent more than a renewed trust and confidence in our public school system, it also reflects great improvements that have been made in recent years — educational as well as capital — combined with the great job our principals and teachers are doing in classrooms and schools across the District every day,” Gray said.