MARIONETTES. Puppet Theatre Barge tries to wean adults and children from TV

The theater rocks with laughter -- literally rocks -- since the theater is a barge bobbing gently in a canal off the Thames. The performers, a set of monkeys dangling from strings, don't miss a beat, but hurl themselves into another round of antics.

The Puppet Theatre Barge, which cruises the Thames between Oxford and London during the summer, is going against the entertainment currents as it tries to wean both children and adults away from their televisions and back to the ancient art of the marionette, if only for an hour or two. It is also a unique diversion for travelers along the Thames during the spring and summer, and for visitors to London during the gloomier months.

In style, the Movingstage Marionette Company (proprietor of the Puppet Theatre Barge) is a highly conservative outfit. Not only does it employ string puppets, a centuries-old genre, but it works with small marionettes in an intimate space, the way marionettes were seen by royalty and the aristocracy in the 18th century. The larger puppets came along in the 19th century when marionettry became a genuinely popular theatrical form.

In content, though, the shows presented on the barge are anything but traditional. Owner-operators Grenville and Juliet Middleton favor material that is both older and younger than the fairy-tale fare so typical of puppet repertories. Movingstage productions range from medieval tales (``Thomas the Rhymer,'' ``Sir Gawain and the Green Knight'') to Shakespeare to the 20th century.

The Middletons also throw in some delightful nonsense for young children, such as ``More Monkeys,'' the show featuring the primate acrobats performing inhuman stunts.

The haunting ``Butterfly's Spell'' typifies Movingstage's work. A fable in the true sense, Lorca's dramatic poem is a meditation on love, set among insects in a meadow. The script is full of intense imagery and flights of metaphor; it certainly isn't intended for children, although the insect-puppets themselves are fascinating enough to keep older children entertained. The marionettes are beautifully crafted, the technique competent, but unexceptional.

What stands out about ``The Butterfly's Spell'' is the ambience that Movingstage's puppet masters can create with their little wooden figures. Some of this is owing to the eerie, original music composed for the production, and some to the effective, moody lighting and set.

The Middletons spent three years touring puppet shows in the conventional manner, by truck and trailer. But they ran up against a problem that plagues many puppeteers; few performance spaces are well-suited to puppets. ``What really came home to me,'' says Mr. Middleton, ``is that the venue is part of the show. When people enter your area, that's when the show really begins.'' A large, impersonal auditorium dwarfing the scale of the puppets, can seriously undermine the effectiveness of a performance before it begins.

Somehow, the Middleton's thoughts turned to water. They were lucky enough to find a 50-year-old Thames barge, and did all the retrofitting themselves. They now have a cozy and extremely intimate theater, suited perfectly to the diminutive stage, and audiences can feel themselves to be in a special space from the moment they walk up the gangplank.

The Puppet Theatre Barge is moored from October to April on the Grand Union Canal at Camden Lock in London (near the Camden Town tube stop). Then the Movingstage company casts off, journeying up the Regent's Canal and then up the mainstem of the Thames as far as Oxford. The slight rocking of the theater, and the smells of the river or the coal fire add to the atmosphere.

During the rest of the spring and summer, they work their way slowly downriver, stopping in towns for a week or two and playing special engagements for shorter periods. Generally, the barge comes to rest for extended performance series at Oxford, Henley, Marlow, Kingston, and Richmond before returning to London.

The Movingstage company has an extensive repertory, and can pull out any of a number of shows as the occasion warrants. Those likeliest to be on view during the present season, in addition to ``The Butterfly's Spell'' and ``More Monkeys,'' are ``Thomas the Rhymer,'' ``The Ancient Mariner'' (drawn from the Coleridge poem), ``Sir Gawain and the Green Knight'' and ``Bottom's Dream,'' a long excerpt from Shakespeare's ``A Midsummer Night's Dream'' including all of the portions dealing with the fairies and the ``mechanicals'' (the rustic actors). The company's next production, which it hopes to have ready for the winter season in London, will be a full-scale rendition of Shakespeare's ``The Tempest.''

The Puppet Theatre Barge can be a bit difficult to catch up with during the summer months, but its whereabouts and performance schedule, summer and winter, can be obtained by calling 249-6876.