THE TROUBLE with Shaw is his lack of subtlety. He never learned to settle for a chuckle instead of a guffaw, to suggest an idea instead of pounding it into the viewer's head, to be inspirational rather than pedantic. You can try to ignore the propaganda in plays like St. Joan or Major Barbara, which have something of a plot line, and at some points in them you can even ignore the bad jokes. The three plays which opened this week at the Loeb Drama Center, on the other hand, go a long way toward showing how bad a really bad Shaw work can be.

The plays at the Loeb represent a large time span in Shaw's life, from his prime to just two years before his death, when he seems to have been overtaken by senility. In Good King Charles' Golden Days is certainly the most interesting play about the Exclusion Crisis and the social problems of the Stuart Restoration I have seen. Its major problem is that it is not so much a play as an essay in social history. It takes the form of a conversation in Isaac Newton's living room, with Newton, the Quaker George Fox, the artist Godfrey Kneller, James II, Charles I and three of his mistresses taking part. They talk about the state of the Anglican Church, the function of the monarchy, and the date of the Creation. This chitchat is followed by a second act in the form of a dialogue on the nature and purpose of kingship between Charles and his wife. The philosophy is all very interesting, but it would have been nicer if Shaw had included at least a plot to spice things up.

If anything could make King Charles look good, it is the second production, Village Wooing -an unimaginative, and rather pointless tale about a thoroughly boring shop-girl's efforts to snare a pompous, Oxford-educated guidebook writer. In the end she succeeds, but no one, including Shaw, really cares. The play is just a vehicle for him to get in a few anti-American one liners, and express his male chauvinism more thoroughly than in his other plays.

Farfetched Fables is the most disappointing of the three plays, because, at first, there seems to be some hope for it. Written in 1948, it starts with a few well chosen and bitter words about Hiroshima and the atom bomb. It soon becomes evident, though, that even if Shaw's sense of outrage grew fierce in his old age, he never learned to temper his sledge hammer blows. The polemical tone of the play, which lectures the audience as if they were mad war mongers with the intelligence of six year olds, is both offensive and unpolished. Thus Fables, which had more promise than the other two works, ends up the biggest disaster of the three.

There may be a good reason why the directors (Robert Chapman and Eleanor Lindsay) of these productions decided to stage them as "dramatic readings," but if there is they are keeping it carefully hidden. The effect achieved by a group of fully costumed actors pacing around Jonathan Miller's simple and beautifully effective sets with loose-leaf notebooks in their hands is absurd. The actors who have taken the trouble to learn their lines are encumbered by the unwieldy scripts, and the others get tongue-tied and lose their place anyway.

By and large, the quality of the acting in King Charles is much better than in the two short works. Michael Smith is a convincingly dissolute Charles with a remarkable presence, and John Paul Russo's Newton is a marvelously mousy character who contrasts sharply with the strong willed Newton shown on a slide at the back of the stage. In general, the device of contrasting the actors with the likenesses of the characters they portray is effective and helps occupy the viewer's mind during the long dry stretches. The three mistresses are well done, especially Pamela Walters' Nell Gwynne, who flounces about the stage like a first-rate floozy.

The two characters in Village Wooing are both well played. Natalie Lombard as the vacuous showgirl gives a good rendering of a cardboard role, and Martin Andrucki is sufficiently pompous as the guidebook writer. The acting in Fables, on the other hand, is an almost unmitigated disaster. Delia Sang gave a good performance in the first and third fables, but almost everybody else was uniformly awful. As bad as the script was, there were places, like the fourth fable, where the acting made it worse. But by then, no one gave a damn.