ALMOST EVERY living actor and actress has had a go at A.R. Gurney's ''Love Letters,'' everyone save Ruby Keeler and Cesar Romero, but then the decade is still young.
It's no wonder. The play is immensely attractive to actors. All they need do is sit for some 104 minutes (save for one 20-minute intermission) and read letters.
It's also a very good play. In those 104 minutes, we get drama, comedy, tragedy and joy, all the things needed to make a complete evening in the theater.
Gurney is the playwright who has become recognized as the official dramatic spokesman for the American WASP community. His characters attend private schools, own horses, marry and frequently divorce, and travel extensively abroad.
You don't, however, have to be WASP to identify with Gurney's people, particularly these two. They may have more money than most Americans, but it is easy enough to relate to them. Colleen Dewhurst and George Hearn have the roles at the Mechanic Theatre, where ''Love Letters'' opened last evening.
She is Melissa Gardner, and he is Andrew Makepeace Ladd III. They meet when they are in the lower schools.
They begin to correspond from the very beginning. They become friends and no more, at least for a time. They try for romance, but it doesn't take, mostly because she is not interested in him as a potential lover.
Over the years, she marries twice, has two children and divorces twice. She also spends a lot of time in homes for alcoholics, drying out. He, meanwhile, serves time in the Navy, becomes a lawyer, marries, has three sons and becomes a senator.
It is at this point that Melissa and Andrew realize they love each other and consummate their relationship. Both, however, know the relationship can go no further than this.
''Love Letters'' is about life, love and the quest for fulfillment. It is a tale that is both humorous and moving. It is all the play you need.
It was first done at the New York Public Library. Later, it was done in New Haven, Conn., then it returned to New York where it was performed at both the Promenade and Edison theaters. It has also played all over the country.
Dewhurst did the role when the play was done at the National in Washington last fall. Hearn did ''La Cage Aux Folles'' and ''Sweeney Todd'' on Broadway. Both are excellent performers. All this may look effortless, but it isn't. ''Love Letters'' makes its own demands, and Dewhurst and Hearn meet them.
''Love Letters'' will continue at the Mechanic through May 26.
*** Melissa and Andrew, friends since childhood, continue a correspondence through their adult years.
CAST: Coleen Dewhurst, George Hearn
DIRECTOR: John Tillinger
RUNNING TIME: One hundred and four minutes with one intermission.