The Montgomery County school board added $12 million yesterday to next year's capital projects budget, with the bulk of the funds to be used to speed the construction of two elementary schools for the Gaithersburg-Germantown area.

Overwhelmed by a rapidly growing number of elementary students in the area, school officials have been under increasing pressure from community leaders to build new schools quickly to relieve crowding. Lake Seneca Elementary, which opened this year, has room for about 700 students but already has 920 students with enrollment expected to grow to 1,200 by fall.

The board's increased funds also include about $1 million for construction of a new Area 3 administrative office building in the northwestern part of Montgomery County.

Area 3 administrative headquarters are currently at South Lake Elementary School in Gaithersburg, which will soon be converted into classroom space for the growing numbers of students.

Philip Rohr, director of the Department of Facilities Planning and Capital Programs, said elementary school enrollments in Montgomery County will grow from about 40,000 in 1983 to about 60,000 in 1991. Most of that growth is taking place in the Gaithersburg-Germantown area, where enrollments are expected to grow from about 17,000 this year to about 26,000 by 2000, school officials said.

Only two new schools have been built there since 1975, Rohr said.

"We're playing catch-up," he said. "One of the reasons we're speeding up the capital program is so we can get the schools there when the kids are there or before they arrive."

The additional $12 million brings next year's total capital budget request to $102 million. School Superintendent Wilmer S. Cody had originally proposed a capital budget of $90.4 million.

The council has until May 15 to adopt the school system's capital and operating budgets.

The original request included two elementary schools, Darnestown-Travilah and East Germantown, both scheduled to open in 1987, and for a new high school in the area.

The amended budget now also includes construction money for North Germantown Elementary School and Montgomery Village-Laytonsville Elementary School, both to be opened between September 1987 and January 1988, instead of a year later.

The board members also added an extra $720,000 to the capital budget to renovate the 30-year-old kitchen at Gaithersburg High School.