IF YOU GO to the Loeb this week, you have nothing to lose but your mind. And that might be the best thing that could ever happen to you.

Whites, blacks, radicals, liberals, conservatives, heterosexuals, homosexuals, sado-masochists, women-liberators, male chauvinists, Wellesley girls: Moring, Noon and Night will freak you all out. There will be fist-fights at the Loeb this week; nasty words and name calling; walkouts galore. Something is happening over there, and that something should not be missed.

Exactly what is happening on Brattle Street are three one-act plays, all written by young Americans and all deeply rooted in the nightmarish decade that is now grinding to a halt. A decade of snipings and war, assassinations and drugs, Tiny Tim and Aretha Franklin- Morning, Noon and Night is not so much about these things as of them. And such is the stuff we are made of- we and night mares.

The first of these one-acters, Israel Horovitz's Morning, is black in every sense. The set and costumes are black, the people are black (or white, as I'll explain in a second), the humor is black. It is a strange play, one that insecure whites and Uncle Toms will call racist. Don't believe them.

Horovitz has set the work in Harlem, on one particular morning when a black family of four wakes up to find themselves as white as the sun outside their 125th Street window. They achieved this color transformation, you see, with the help of some amazing pills sold to them by a Jewish pawnbroker who got them from God (who is black), (Or maybe you don't see- it doesn't matter.)

Anyway, with the help of these pills, this family has now escaped forever the sorrows of being black in America. As Gertrude, the mother, puts it, "I'll mince my way through Macy's and get thirty day credit. No-000000 one will give me crap."

The only hitch in this family's freedom is a white liberal, Tillich ("I've seen Guess Who's Coming to Dinner," he say. "Twice!" ), who arrives on this morning to murder some "black bastard" who knocked up his daughter. Tillich is rather upset to discover that the black boy he had expected to kill is now white. And, as he and the family play some explosive power politics during the course of the play, the family gradually arrives at the conclusion that "black is beautiful" after all.

PLAYWRIGHT Horovitz lets everyone have it in Morning. The play's language- explicit and, as they say, coarse- will probably send a good deal of people out of the theatre within a few minutes after the house lights dim. And the playwright's handling of dialects (The white actors switch back and forth between Harlemese and East Side-esque.) is bound to scare a lot of whites into silence as the play goes on its hysterically funny way.

Indeed, I suspect particularly uptight whites in the audience will search for a black in the theater- and wait for him to laugh before they do the same. This is because many whites simply don't know how to react to blacks as people yet. When most liberals hear the black-cum-white characters in Horovitz's play putting on Butterfly McQueen accents, a sign lights up in their minds saying "Racial Stereo-types. . . Gone With the Wind. . . Racist" -and the liberals freeze.

And that is the whole point of the play. Race relations in this country have still not advanced past the point where most whites can conceive of blacks as anything other than types, whether they be "good types" or "bad" ones. Blacks are placed in a "Stepin Fetchit" box or a "Stokely Carmichael" box or a "white" box or a "Sidney Poitier" box. The thing is that no black- or no human being, for that matter- ever fits into any box. As Morning's family changes its voice from an Amos'n' Andy inflection to a John Lindsay or Wilson Pickett or Rap Brown inflection, the white audience is scared out of its wits. It doesn't know how to react. (The suburban liberal in the second row tells himself each time a character says "Shee-it" : "I can't laugh at that- it may be funny, but everyone will think I'm a racist.")

In this way the characters manipulate the audience. The audience will react to every linguistic image-every "box"-while totally forgetting that the people on stage are human beings having nothing to do with the way they talk. Many old liberals will be so hung up on their knecjerk reactions to dialect that they will fail to deal with these people on the basis of anything but those superficial bases for which they have Pavlovian responses. The audience will be too screwed up-and frightened-by the play's complex inverted humor to listen to the words- or laugh.

It is perhaps a cruel joke Mr. Horovitz is playing on the theatregoer- but a necessary one. It is exactly the kind of communications impasse he is dealing with that spawns the rhetoric that leads to real racism, law-and-order candidates, blacklash and violence. It is no surprise that his play ends with a grotestquely scary and ecumenical ("Kill the white man! Kill the black man!") chant of murder.

TERRENCE McNALLY'S Noon does not have the apocalyptic ending of Morning, but it deals with very much the same problem in a different context, that of sex.

Surely one of the funniest one-acters I have ever seen, Noon is about a wide variety of people (a nymphomaniac, a homosexual, an uptight heterosexual-intellectual, and a middle-aged sado-masochist couple from Westchester) who find themselves thrown together in a New York loft. They have all come to meet with a certain Dale (sex unknown) who seems to have answered each character's sleazy newspaper ad for sexual adventure.

But Dale does not show up- and what follows is one of the great non-orgies of all time. Only in the sixties, in the days of the so-called sexual revolution, can people of such widely varied sexual tastes come together- only to find that none of their tastes coincide. Like Horovitz, McNally powerfully demonstrates how the multitude of roles available to liberated modern man can become a humanity-crushing obsession.