Opulence, energy, family fun -- that's Le Grand David and his magic troupe

In the middle of the downtown area in this modest-size city about 20 miles from Boston stands a rather ordinary-looking movie house. What happens inside is far from ordinary.

For over five years the Cabot Street Cinema Theater has been bursting open each week with a resident show packing enough opulence, energy, and wholesome family fun to attract a national following. That's no small accomplishment for any company of performers, and especially not for ''amateurs.''

But this company has something special. They have - well, magic. In fact, their show is called ''Marco the Magi's Production of Le Grand David and His Own Spectacular Magic Company.''

The 70-member company has received ample recognition. To mention just a few honors, Marco the Magi was named magician of the year for 1981 by Hollywood's Academy of Magical Arts. Last Easter part of the company traveled to Washington, D.C., to perform at the annual White House Easter Egg Roll. And they gave their 650th performance on May 30.

Persistent offers for Le Grand David to tour have been turned down. ''Why should we tour?'' asks Webster Bull, president of the organization (and brother of David Bull, who is Le Grand David). Since sellout audiences already come to them from other parts of the country and even the world, the difficulties involved in putting the complex production on the road hold little appeal.

And although the company is a profitmaking business, he says, the well-being of the children and the families in the organization weigh heavily in decisions.

From the moment the tassel-hatted clown escorts guests from the mouth of the welcoming dragon at the door to the last dazzling sleight of hand, the audience has been lavishly and generously entertained. Its blend of humor, warmth, and joie de vivre makes Le Grand David much more than a magic show: It offers music, comedy, and dance.

Three ''generations'' of magicians are dramatically ''unveiled'' at the beginning of the show after a parade of exotically dressed company members drifts across the elaborate stage and through the mist that wafts out into the audience. The audience soon learns, however, that the patriarchial Marco, the dashing David, and winsome 10-year-old Seth the Sensational have more enthusiasm than mystery.

According to Marco - who off-stage is Cezareo Pelaez, a professor at the local state college in Salem, Mass. - ''We've defined the characters so that they are happy, joyful, and in celebration. If it's not fun for us, how can it be fun for the audience?''

Professor Pelaez should know. He's the founder and mastermind behind the show. As a child in Cuba, he saw many of the great South American magicians. But his conception of magic is much broader and more theatrical than performing magical acts.

''What we want is the aliveness, the sense of wonder, which is the qualitative part of a magician, and that's the magical moment.

''We don't claim to have any supernatural powers,'' he asserts with the pleasant Cuban inflection that gives an additional aura of the exotic to the show. ''What we do is often called tricks.''

David Bull adds, ''There are things that Marco has insisted on. If you vanish something, you always bring it back.''

Remarks Webster Bull: ''What a magic company is is a whole host of performers of all kinds . . . dancers, singers, clowns, actors . . . . And magic becomes the vehicle, or perhaps the channel, for a theatrical experience.''

One of Le Grand David's big fans is Robert Lund, founder and director of the American Museum of Magic in Marshall, Mich. He has followed magic for almost 50 years and has been a collector of magic objects for almost 40.

''I tell everyone that it's the finest magic show that I've ever seen, and I've seen hundreds. No magic show has built (its) equipment with the attention to detail that Le Grand David has.

''There's no violence or cruelty involved. There's no danger, and no sawing ladies in half.'' He adds that Marco the Magi has the magic performed on himself. ''Children know that no harm can come to that man.''

At one point a huge papier-mache dragon prances through the auditorium, its turquoise eyes flashing at the audience. ''It's a friendly dragon,'' remarks Pelaez. ''It once was able to shoot out fire but a child was scared. We don't use fire anymore. Who wants to spend a day being scared.''

Often there's more than can be taken in at once on stage of elaborate costuming, richly decorated props, and magical activity. In fact, if Le Grand David has erred in any way it is in being overly generous with the number of acts during this 21/4 hour show.

But throughout, the audience sits in enthusiastic silence in their seats, proving it's not necessary to shock to entertain. Despite Le Grand David's powerful appeal for children, performances draw an overwhelmingly adult crowd, according to Webster Bull.

Behind the magic goes plenty of hard work. The company uses the stage and a series of colorfully decorated rooms above the theater that the public never sees for practices.

Timing is vitally important, particularly for Marco the Magi, who is involved in most of the more than 50 stage illusions and who at last count used 68 costumes each performance. The movements on stage of the supporting members of the company are choreographed to lend both grace and support to the show.

Because every member of the company appears on stage at some time, the clown who ushers before the show begins may very well perform in the band of the dark-suited trumpeters, and then return later as a clown.

Almost all of the costumes, props, and curtains are made by the company. During the week, much of the company is also busy with other pursuits. Tassels the Clown, for instance, is David Feldman the high school teacher. Part of the papier-mache dragon that tromps through the auditorium becomes a vice-president of a bank.

The presence of children is particularly important during the show. Seth, whose last name is Bartlett, has been a featured part of the production since the beginning. He is joined on stage by 14 other children at various times.

Also important is the Cabot Street Cinema Theater itself. Built in 1920, its plain exterior contrasts with a rich interior. Hands that help Marco disappear and reappear have painted, nailed, and plastered the 956-seat theater back into it's original luster.

Remarks Webster Bull, ''I like to think that this is a big city theater plunked down in the suburbs.''

When the magic stops (the performers give matinee and evening performances on Sundays), the Cabot Street Cinema Theater returns to being a movie house, a place to catch revivals of old films and recent releases.

But it's Le Grand David that makes audiences magically appear and fill a grand theater tucked away in the modest city of Beverly.