Super 8 films become a medium for serious expression.

Super 8 film - the kind you can buy in handy, inexpensive cassettes at your local drugstore - is associated in most minds with home movies projected on sheets in living rooms or with bank surveillance films, and it is greeted with hilarity by members of the commercial film industry.

But in recent years Super 8 has come to be regarded as a medium for serious expression. For five years now an international Super 8 film festival has been held in major cities around the globe, including Caracas, Brussels, and, last Feb. 21-26, in Montreal.

The 1984 festival was sponsored by the Canadian Broadcasting Corporation, administered by the Association pour le Jeune Cinema Quebecois in collaboration with the Association Montrealaise du Jeune Cinema - organizations devoted to promoting young cinematic talent in Canada. It was held in the Cinematheque Quebecois, a major film research center and museum.

The participants, linguistically split between French and English, came from across the globe. They ranged from film professors to presidents of amateur film societies, from student filmmakers to professionals, from Joseph Morder, a French baker who makes ''personal'' films, to Pierre Payant, technical representative of the cinema and audiovisual division of Kodak, Canada.

The technical quality of most of the films - a mixture of fictional, documentary, and experimental works, many produced on microscopic budgets - was amateurish, although conceptually they were no more or less imaginative than most multimillion-dollar Hollywood products. Perhaps not surprisingly, some of the most technically polished pictures came from the Soviet Union, which has a lavishly subsidized, professionally administered network of amateur ''cine-clubs ,'' and some 350,000 8-mm filmmakers.

But what was fascinating about the international entries was not technical expertise, but how Super 8, by its accessibility and compactness, enables artists to make personal and political statements possible in no other medium. Even some of the more obscure ''experimental'' films packed an explosive political punch. In the 4-minute color film ''Blue Tropical,'' by Poli Marichal, a Puerto Rican - which won first prize with a German entry - one saw images of fire: Apparently they were veiled references to an unreported police raid in which squatters were driven out and their homes set ablaze, and of the symbol a of star literally hand-scratched on the emulsion of the film.

Reinhard Wolf, a German filmmaker from Mainz who judged the festival entries, argued that Super 8 is ideal for depicting controversial issues such as the German squatters' movement, ''because those issues are often things which happen in situations where you can't come with a great camera team. . . . You would lose the trust of the people. . . . But you come with a Super 8 camera into a squatter's house, they'll let you in. . . . You couldn't do it with a large camera.''

At the festival there was a great deal of talk about ''direct cinema'' - a form of documentarymaking in which the filmmaker enters an event or situation with the aim of recording it with as much ''objectivity'' as possible. One example was the sensitive ''A Bordo de un Carrito,'' a film about handicapped athletes. But Reinhard Wolf opposes direct cinema, preferring to use Super 8 as a means of fusing documentary and fiction. In an interview, Mr. Wolf described a Super 8 film - not shown at the Montreal festival - on the German antinuclear demonstrations in 1982, which he made in collaboration with other filmmakers and some 20 German film groups in and around Bonn, Berlin, and Essen.

''We wanted to make a reflection about this (peace) movement, not only showing that they are powerful, that they are many - that is obvious. But we tried to analyze the motivations and the strategies of the opponents. This was the time of the NATO summit in Bonn. So what we did was, we split up the production team, and everybody had a special task - a sector of the town, maybe - or a special subject to watch. One had to watch for the helicopter which brought in Reagan . . . .

''And after we took this documentary material we looked at it and we tried to find out what was missing . . . then (fictional) stories were written and narrated . . . .

And we integrated the story into the documentary part.'' Toni Treadway is a filmmaker from Somerville, Mass., who, with her husband and collaborator, Bob Brodsky, specializes in transferring Super 8 to videotape. She says that, as represented at the Montreal festival, Super 8 ''is an incredibly important political phenomenon. . . . Super 8 is the only medium where people can make whatever images they want to make and have any kind of economic accessibility. People who work in 16 mm have already gotten to the level of being able to accumulate resources, people power, equipment, money, but it seems like you have to be a little bit beholden to the resources. There's no such thing as money without strings.''