George Washington University, whose officials long have expressed a desire to move some of the school's facilities out of the District, announced plans yesterday to build a major instructional and research center near Dulles International Airport.

The center will be located on a 576-acre tract in Loudoun County near the Fairfax line. It will be developed by two of Washington's most prominent builders as a commercial research and office park, and will be somewhat similar to research parks developed by businesses and universities around the country.

The university said developer Michael Swerdlow and the Charles E. Smith Cos., which recently purchased the entire tract for $26 million, had donated a 50-acre parcel at the site, just west of the intersection of Rtes. 7 and 28. The land, once owned by Marcus Bles, a well-known Northern Virginia land speculator, is considered to be one of the most valuable parcels of vacant land in the rapidly developing corridor around Dulles.

Lloyd H. Elliott, president of the 17,000-student university, said in a statement that the project was a logical extension of GWU's "traditional mission to offer our academic programs at convenient locations throughout the region while maintaining our main campus in downtown Washington."

Three years ago, a school committee called for the university to acquire property in the suburbs in an effort to improve its relations with business groups. A spokesman for the school, whose 90 buildings are in Foggy Bottom, said the university is committed to retaining its main campus in Washington.

"There's absolutely nothing to the suggestion that this would diminish our efforts at the main campus downtown," said spokesman Barry Jagoda. "The Virginia center will only add to the strength of the university."

Elliott said the Northern Virginia center will furnish area industries "with a solid base for applied research . . . and students with experience in working with industry-related research."

The first building at the Loudoun site will cost $10 million and will open for classes in the fall of 1989, officials said. The 70,000-square- foot center will be used for graduate studies and research for the school of engineering and applied science. It will contain laboratories and support services for 500 students and 20 staff members.

"We expect to grow," said Charles E. Diehl, the university's vice president and treasurer. "I don't think we'd be going out there if we expected to stay at 70,000 square feet."

The university's announcement said that within five years the school expects to have about 200,000 square feet of office space in Loudoun County and that its long-range projections call for "expanding to the maximum permitted on the site."

Diehl declined to discuss how the private university plans to finance construction of the new facilities, saying only that several funding options are being considered.

Diehl said the university's expansion into the Virginia suburbs is not intended as a challenge to George Mason University, a fast-growing, state-supported school in Fairfax County that has made a determined bid to grow with the support of businesses in the area. "I don't think you can look at this in terms of a competition," said Diehl. "I think it will be complementary to George Mason."

J. Wade Gilley, a senior vice president at George Mason, seemed to agree. "I don't think what they do will have any effect on the size of our school or the quality of our students," he said. "Our engineering school is designed to be fairly specialized and relatively small, and our demand in Northern Virginia is huge."

Officials at the Smith Cos., which developed much of Crystal City in Arlington, said it was premature to discuss details of its plans until zoning changes were obtained.

The site is zoned for various uses, including agricultural, residential and low-density industrial, according to Loudon officials.

University officials said that they expected it to take six to nine months to secure the necessary zoning changes.

Wilbur Levenper, a Smith Cos. vice president, said his company and Swerdlow were considering a development with a mixture of uses, including offices, research laboratories, student housing, a hotel and retail stores to complement the university facilities.

Loudoun officials hailed the project, saying it would produce substantial tax benefits and act as a magnet for other developers. "The addition of a university of that caliber improves our quality of life and our industrial base," said Supervisor Frank Raflo of Leesburg, a member of the county board.

"I'm delighted with it," said Supervisor Ann B. Kavanagh. "It will be a very big asset to the county."

Both Raflo and Kavanagh said that they expected the proposal to encounter little opposition and that the county probably would grant the necessary zoning changes.

Marcus Bles, who is dead, once owned the farm land on which the project is planned. Bles also owned the land on which the Tysons Corner Center shopping mall is located.