The Minikin Opera Company, one of the world's smallest, breezed into the Adult Education Center of the University of Maryland last night and presented two operas using a total of six singers and one pianist. The scenery consisted of a few flats, self-supporting and reversible, with one side providing a set for "The Boor," by Dominick Argento, the other for "An Incomplete Education," by Emmanuel Chabrier.

In front of those sets, with orchestral effects supplied by pianist Steven Mosteller, transpired an evening almost totally lacking in substance but well-stocked with entertainment.

Based in Wilmington, Del., the Minikin is opera stripped to its basics, designed for maximum mobility. Everything it needs for a production (except the piano, which must be supplied by the hosts) can be carried in a single van, and it can and does perform almost anywhere from a gymnasium to a living room.

Its productions are short, melodious and sung in English. It may have relatively little impact in a city where the Metropolitan has just left town, but in many parts of the Middle Atlantic States, it is the only live opera some people ever get to see. Its productions are simple, without frills, but thoroughly professional.

"The Boor" is the story of a widow jolted out of her year-long mourning by a rough-hewn but (ultimately) lovable neighbor. It has a wealth of fine melodies, well-adapted to the natural cadences of the English language, and it was generally well sung, though soprano Kim Steiner sometimes had a bit too much vibrato and too little clarity of diction.

Tenor Nathan Gable as her servant had a fine, clear tone, and baritone Carmen Muni, as the neighbor, tended to dominate the stage vocally and dramatically when he was present.

In last night's performance, the opera seemed a few minutes longer than optimum--possibly because the stage direction was less lively than in Chabrier's "An Incomplete Education," which focuses on the problems of a bride and groom, both uncertain of how to begin their honeymoon.

The casting and pace in the Chabrier seemed almost ideal for what is essentially a short farce with spoken dialogue and lots of light, attractive music.

Tenor John Kennedy was charmingly wimpish as the groom, Elena Clancy vocally and theatrically winsome as his willing but ignorant bride, and baritone Robert Wallace, imposing as the teacher who thought conjugating was something you did to Latin verbs.