A consortium of Washington area universities will announce plans Monday to build a $21 million computer-linked "superlibrary" in Prince George's County, creating the third largest academic collection in the country behind Harvard and Yale.

Initially accessible only to students and faculty of the participating schools, the proposed library would be the first venture of its kind nationally, combining books and periodicals from eight individual schools under one roof.

Consortium officials, Rep. Steny H. Hoyer (D-Md.), County Executive Parris Glendening and a top U.S. Department of Education official will make the formal announcement Monday, in addition to unveiling an undisclosed companion project.

"The gist of it is, universities in the Washington area are competitors, but they also can cooperate," said American University President Richard Berendzen, whose school is participating in the project. "It's just a tremendous step forward for academic institutions in the Washington, D.C., area."

Creation of the library is contingent, in part, on the organization getting $7 million from the pending appropriation bill in Congress for the departments of Labor and Health and Human Services. The remainder of construction and operating costs would come from the universities, private sources and Prince George's government.

The library, still unnamed, eventually would house more than 5 million volumes, compared with Harvard's 10.5 million and Yale's 8.3 million. Additionally, it would provide computer access to another 16 million library holdings at the individual school libraries in the District, Maryland and Northern Virginia. It would not rival the Library of Congress, which holds more than 80 million items.

The eight universities that make up the consortium corporation are American, Georgetown, George Washington, Catholic, George Mason, the University of the District of Columbia, Gallaudet and Marymount.

Under the plan, students and faculty members at the participating universities would be able to use 1,200 computer terminals placed in campus libraries, academic offices and dormitories. After searching through an electronic card catalogue, students would request a book or periodical. A fleet of vans would deliver books to the school libraries, on the same day in most cases.

The plan for a superlibrary was born three years ago as local college presidents sought ways to control the high cost of library construction, book preservation and scholarly acquisitions.

The Rev. John P. Whalen, executive director of Washington's Consortium of Universities, the parent organization of the corporation that hopes to operate the library, said a central depository would save money by eliminating duplicate book purchases and forestalling the need for new construction.

"Monies saved could go into collection enhancement instead of building all of these marble boxes to house books," Whalen said. Schools would donate between one-fourth and one-half of the volumes currently in their libraries, most of them obscure or rarely used works.

Berendzen said educators estimate that only 20 percent of their library holdings are used regularly. "We all have volumes that are not used much by the average scholar," he said, listing the Australian Journal of Polymer Chemistry as the kind of obscure book that would be available at the new facility.

The facility, at Rte. 301 and Central Avenue, essentially would serve as a warehouse, but there would be research facilities for scholars.

For Prince George's, the decision to locate a research facility of national significance within its borders is a symbol of the county's growing prominence as a leader in seeking out and attracting high-tech companies and educational facilities that can bolster its progressive image. Prince George's also is a contender for a new residential high school proposed by Gov. William Donald Schaefer. "In the future, when people refer to academic research, they will refer to Harvard, Yale and Prince George's," Glendening said. "That, combined with the quality of economic development, reflects the optimism developers have in the county."

The library building would be located on county-donated land at the Collington Center, a 1,200-acre development that is home to a state foreign trade zone and a proposed new commercial development. No opening date has been forecast.

The Rev. William J. Byron, president of Catholic University, said the consortium considered facilities in the District in hope of being near the Metro. The idea was to have student runners transport books. Eventually, though, costs proved prohibitive, he said, and the consortium sought sites that would be easily accessible from the Beltway.

Whalen said Prince George's was selected because county officials were eager to cooperate and provide land. The county donated 20 acres of publicly owned land and will provide technical assistance.

The project also would include the costly deacidification of books, a preservation process that few schools can afford independently. Another benefit of pooling resources is the diversity of materials that eventually would be available. Catholic University, for example, plans to donate collections on religion, and Howard University could place important works on African American studies there.

The University of Maryland is considering joining the consortium, and discussions with Howard are in the final stages, Whalen said.