Beginning tonight, the Loeb will play host to a week-long international film festival organized by a group of graduate students and research assistants from Harvard, M.I.T., and Boston University.

Nearly 50 films from 12 countries will be shown during the festival's run. Only movies not previously screened in this country are eligible for the competition.

A committee of local drama and art critics will write criticisms and award "citations" to the films on the basis of the "specific qualities" of each presentation.

At the end of the festival, a "jury" including Robert H. Chapman, director of the Loeb, and Laurence Wylie. C. Douglas Dillion Professor of the Civilization of France, will award general citations to the most outstanding films.

Separate panels of judges will issue awards for the best features and documentaries entered.

The sponsors of the festival hope to play down the "competitive" atmosphere of the week's program. Instead, the festival will be an attempt to give all producers, large and small, the chance to submit their films for thorough appraisal. No "Commercial or Political Prejudice"

The sponsors also wish to free their festival of the "commercial or political prejudice" which characterize some similar competitions.

Before the awards are announced this Saturday, movies from France, Germany, Canada, Japan, India, Greece, Mexico, the Netherlands, Britain, Italy, and the U.S.S.R., plus 12 American productions, will be shown.

Performances will be held at 5, 7, and 9:30 p.m. each evening, beginning Tuesday. A special screening for invited guests will open the festival tonight. In addition, two films not entered in the competition will be shown at 5:30 p.m. this afternoon.