Students and faculty members at Georgetown University School of Dentistry have filed suit, seeking to block for at least a year the planned closing of the 86-year-old school.

The suit, filed Monday in D.C. Superior Court, charges Georgetown's president, the Rev. Timothy J. Healy, and its board of directors, with fraud, breach of contract and fiduciary duty for the decision to phase out the school by mid-1990.

The university decided in March to close the school because of a looming "financial disaster" and because of fears that its quality would deteriorate as the number of students going into dentistry continues to plummet nationwide. The school, which had 570 students last spring, notified 120 students who had been admitted for next fall that there would be no first-year class and returned their deposits.

A spokeswoman for Georgetown said the university would have no comment on the suit.

In papers, prepared by attorney Arthur B. (Tim) Hanson, the plaintiffs contend that the university violated its procedures in closing the school and that the decision was made with only "limited discussion" and "without sufficient and/or factually accurate information."

The suit asks that the university be required to maintain all faculty positions this fall and teach a first-year class. It also seeks to require the university to prepare an evaluation of the "financial and educational viability" of the dental school, far more extensive than the report by the Price Waterhouse accounting firm, on which it relied in making the decision to close.

Hanson suggested that the university might eventually negotiate with its dental faculty to set up the school as an independent institution, affiliated with Georgetown University Hospital but with no reliance on general university funds for support.

Plaintiffs in the suit include three current students and Dr. William R. Cotton, a professor who heads the operative dentistry department.