Although Kaye Ballard calls her new evening of comedy and song "Working 42nd St. At Last!," the event is actually a cozy house party with clowning Kaye, as usual, vamping the occupants.

The venue - the oddly arranged Kaufman Theater, way west on Forty-deuce - is an advantageous one for Miss B., who has at least three psyches trying to get out of her ample frame at once ("There's more tension in my zipper," says our star, "than there is in Nicaragua"). One is a singer, another an actress and the third is a distaff cousin of Groucho Marx. I love all three of them.Ballard begins a familiar lyric, "Why was I born? Why am I . . . " and ends that last question with: "Playing a theater with two audiences?" She stands in a long, thin auditorium on a stage which bisects her audience, assuring them it was "built for Siamese twins." But as she clowns with a silly song like "I Just Kissed My Nose Goodnight," or creates a glow with some Irving Berlin oldies which we didn't hear during his centennial week, the room works to this artist's benefit. Julie Wilson, for example, didn't fare so well here because she's far less kinetic and frenetic than Ballard.

In many ways, "Working 42nd St. at Last!" is an extended cabaret turn, a charming grab bag of special material, lovely standards and bits of nostalgia which pay homage to the 42nd Street area of yesterday, "The Paramount, Capitol and the Strand."

Kaye Ballard, always more than welcome, this time around makes little reference to her Italian heritage but does, reliably and skillfully, take the flute in hand, deftly reminding us that she's also a skilled musician as well as a singer and comic.

Speaking of music, the stage at "Working 42nd St." is shared with composer-pianist-singer Arthur Siegel, who spells the star in song, and Miss Faun, once of "The All-Girl Orchestra of Miss Faun," and a lady a long time cabaret watcher has described as "the most expressive instrumentalist since Harpo Marx." Kaye Ballard insists, "She brings new meaning to the word bass."

Siegel winningly reprises some of his own songs such as "Love Is a Simple Thing," which he wrote with June Carroll for "New Faces of 1952," and joins in with Ballard on Barry Kleinbort's "Sondheim Song," which promises there will be no such music in "Working 42nd St."

During the two-hour Ballard jamboree, the star amuses the audience with Suzanne Buhrer's cute song, "My Son" ("the stripper"), and Ballard's familiar version of Ray Bolger's old show stopper, "The Old Soft Shoe," from "Three to Make Ready," which she does moving a pair of brogues along a piece of sandpaper. She also brings back memories of the late Mabel Mercer, singing "Remind Me" in three keys at once, this time mercifully omitting that cruel (but funny at the time) cough. And for a change of pace, she again proves her vocal eloquence with John LaTouche and Jerome Moross' "Yellow Flower" from "Ballet Ballads," created in 1948.

From "Burger Beguine," an anthem to fast food emporiums taking over the entire world, to a reprise of Cole Porter's "Tale of the Oyster," with which the singer stopped Ben Bagley's "The Decline and Fall of the Entire World as Seen Through the Eyes of Cole Porter" 33 years ago, Kaye Ballard thoroughly captivates her audiences in this wonderful mini-revue. Bagley, the old "Shoe String" revuer himself, incidentally, serves as creative consultant. It's all very fabulous '50s . . . but still a great deal of fun. And I earnestly suggest you catch Kaye Ballard, "Working 42nd St. At Last!"