Two young playwrights mixed magic and mediocrity in the Experimental Theatre last evening. Marie-France Lathrop's mime--Others, I Am Not The First--was magical. Senior Jonathan Sisson's Minsky O'Ryan and the Magic Bathrobe provided most of the mediocrity.

Minsky O'Ryan and the Magic Bathrobe is not entirely bad. As Minsky, a man who destroys things, Lauent Weisman is very effective. He portrays Minsky with a forceful calm that the play lacks. Richard Black plays his dinner guest, an advertising executive, with the deliberate superficiality the role requires. But it is not much of a role, and Black's jittery movements and exaggerated expressions of joy only add to the chaos of Sisson's play.

The problem is that Sisson has written too much noise and distraction into Minsky. There must be a subtler way of reminding us how destructive life with Minsky is.

One of Minsky's two servants, Virginia Morris, should be singled out: her heavy-footed scampering on and off the stage is more distracting than all the glass she broke. Lastly, the frantic pace of the production increased the confusion considerably.

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There is little to say about Others, I Am Not The First, except that it is pure delight to watch. Some of the actors who were bad or mediocre in the first play, notably Miss Morris, are enchanting in this second one.

The mime consists of four interrelated scenes preceded by "phases," as Mlle. Lathrop describes them. Each phase is an interlude in which Michael Puorro, who is a baby as the mime opens, grows older. Puorro is especially convincing as he discovers his fingers and hands and learns to walk. His symbolic tug-of-war to hold onto life--pulling on an imaginary rope with Norris Eisenberg on the other end--is graceful and agonizing.

Each of the four scenes ("Playing Cards," and "The Bistro," "The Cocktail Party," and "The Graveyard") comes off better than the last. The staging and light-effects, especially for the "Bistro" and the "Graveyard" are delightful.

Not only were all of the players in Others good; most of them were excellent. Weisman, Mlle. Lathrop, Joan Oppenheim, and Puorro deserve the highest praise.

Others, I Am Not The First is one of the finest things the Experimental Theatre has produced. Try to see it, even if you can't get to the Loeb until half-time.