It's really a shame Shelley Winters has decided to leave the cast of Invitation to a March, because she was the best item in this melange of fine acting, funny cracks, old plot lines, and sex in the form of Jane Fonda. Anyone who wants to see a really expert comic performance should run down to the Colonial as soon as he reads this and get a ticket to Invitation for tonight. For on the morrow Miss Winters will be replaced by Celeste Holm, and though Miss Holm is a comedienne of undeniable talent, it is doubtful that she will equal the special tinge Miss Winters brought to the role of Camilla Jablonski.

And it takes brilliant acting, colorful sets by William Pitkin, and clever costumes by Lucinda Ballard to rescue the conglomeration of sorry old saws put together by writer-director Arthur Laurents.

Basically, the plot concerns the efforts of Norma Brown (Miss Fonda) to choose between a conventional fiance who puts her to sleep and a Long Island aborigine who doesn't. In fact, Aaron Jablonski (James MacArthur) awakens Norma with a kiss in the approved Prince Charming fashion to start the ball rolling. The boring suitor's father finds Camilla Jablonski at the Long Island resort spot and re-kindles a 20-year-old love affair. After an incredible period of juggling figures, the old smoothies deduce that Aaron is indeed their joint issue. That Aaron finally wins the girl is of course a foregone conclusion.

Miss Winters, as has been hinted, handles the part of a cheerful unwed mother with both humor and delicacy. The way the part is written, she could come out sounding like a cut-rate whore, and apparently the strain of battling the built-in deficiencies of the role made her decide to quit. Eileen Heckart, as an often Auntie Mame-like Deedee Grogan, handles wise-cracks, insults, and pathos equally well, and looks appropriately garish in Miss Ballard's costumes. Madeleine Sherwood is hateful enough as Norma's mother, and Richard Derr, as the father of many, is grey flannel through and through.

MacArthur is a surprise as an earthy, hard-headed Aaron. And Miss Fonda, besides playing her part fairly well, displays perhaps the best set of curves that will grace the Boston stage this winter.

Stephen Sondheim's "incidental music" is well-advertised but mostly inaudible. In all, it is a miracle that such a patchwork play comes off so well. Miss Holm had better be good.