Marymount University's Loudoun campus is moving up, in more ways than one. By March 1, the campus, barely one year old, will abandon its cramped quarters on the second floor of a Countryside office building in favor of more spacious offices on the third floor. In the process, student capacity will more than double.

The rapid development of and high interest in the Loudoun campus have surprised even the most optimistic Marymount officials, who have been scrambling to find classroom space for the 200 students who already attend. Most courses are graduate-level classes taught at night and on weekends.

The Arlington-based university's move into eastern Loudoun is part of a trend of Washington area educational institutions reaching out to the fast-growing county. In September, George Washington University held its first graduate engineering class at its Northern Virginia center, barely two miles west of the Marymount location.

In addition, a group of Japanese investors intends to open the Washington International University in Virginia at Lansdowne, possibly in 1992. Shenandoah College and Conservatory has been teaching classes in the Leesburg area for years. Northern Virginia Community College has a two-year program in Sterling.

On Jan. 20, 1990, Marymount University's director of continuing education, Ed Parks, was handed the key to the Loudoun campus's current space on Pidgeon Hill Drive. He had a matter of days to recruit students, and on Feb. 14 the first graduate classes began.

He hasn't had to recruit many students since then. Parks is juggling schedules to make the best use of the three existing classrooms and is borrowing space from neighboring businesses to accommodate demand.

The campus started out teaching graduate-level courses almost exclusively, but it has added junior- and senior-level undergraduate offerings during the past year in response to high interest.

"We've had about 2,000 requests for catalogues in the past year from undergraduates," Parks said, noting that more than 90 percent of his students live or work in Loudoun and that there is pent-up demand in the county for higher education.

Marymount, which also offers courses at small centers in Reston and Tysons Corner, has noticed an increase in enrollment attributable to state budget cuts that limit offerings at public schools such as George Mason University, said Molly Cromwell, vice president for university advancement.

At Marymount's Loudoun campus, "Efforts are being made in strengthening the faculty" to accommodate the expansion coming this spring and beyond, Cromwell said.

Walls are being added and knocked out on the third floor to provide six classrooms, a small job center, a kitchen, a library, a bookstore and an office for Parks, who runs the Loudoun campus. Parks expects to hold the first class in the new location March 9, possibly a course that will be moved there from another satellite facility.

With creative scheduling, the new space could accommodate as many as 500 students, Parks and Cromwell say, though it's still not clear what will happen when the center outgrows its new location.

"We aren't even talking about our own building at this point," Cromwell said. The current expansion phase is something that was "beyond our wildest dreams" when the campus opened last year. Last February, "We sort of sat here and thought, 'Will anybody come?' " Cromwell recalled.

Parks said he intends to offer a master of science in management program that will emphasize technical skills aimed at the current job market. Many of this semester's courses are in the business administration program, with additional offerings in education, human resources and psychological services. A summer session will begin in May.

That month, the Loudoun campus intends to award its first four master's degrees, with 10 to 20 more graduate degrees expected to be conferred in August.

Founded in 1950 as a women's school, Marymount now has nearly 25 percent male enrollment. More than one-third of its 3,000 total enrollees are graduate students, who pay $285 a credit hour.