A VISIT to a bad show doesn't have to be a total loss. For one thing, you can learn the difference between a flop and a failure. A flop, in the words Walter Kerr used a few years back to describe a fiasco called Kelly, is "a bad idea gone wrong." Such a show, through its total ineptitude, can often be very funny. (A knowledgeable friend of mine who saw Kelly's one and only Broadway performance counts it among the most hilarious evenings he's ever spent in a theatre.) A failure, on the other hand, is a good idea gone wrong. It's usually boring.

On paper, Dear World, the musical prepping in Boston for its New York debut, has a promising premise, one that could even be exciting in the execution: an adaptation of Jean Giraudoux's Madwoman of Chaillot with Angela Lansbury as the title character. On stage, though, it's a failure and not a hell of a lot of fun.

Many people make mistakes when a complex production such as this one goes wrong. In Dear World's case, high among the guilty is producer Alexander Cohen, who has hired all the people who make the fatal errors. While Cohen has gone with talented men who hold some of the best track-records in the business, he has hired them for the wrong show.

Among those he has picked, Jerry Herman, the composer-lyricist has the best credentials for success (Hello, Dolly and Mame). Still, this time he is out of his element. Chaillot, even as embodied in this musical, is not the completely frivolous comedy Herman has worked with in the past. Although essentially telling us the story of a comic woman who refuses to accept the fact that the modern world is a different place than it was in 1903, Giraudoux has more than frivolity in mind. Below the surface of his comedy is the serious warning that the snowballing forces of materialism, fascism and war must be checked if the human race is to survive. When Herman's turn comes to dig into this serious core, he falls apart. His answer to the dramatic problem is a song called "Garbage," and it's not much better than the title suggests: a supposedly bitter number about the decline in beauty of refuse through the years. While it might make for some laughs (as it does in the original play), garbage is not the stuff of which pathos is made.

HERMAN has another difficulty; his memory is too good. What he remembers working in his earlier hits, he feels can also work in Dear World. In Mame, the title character tells her nephew in a song "to open a new window" every day to get the most out of life; in World, the Madwoman tells the romantic lead the same thing (in the song "Each Tomorrow Morning"). The first act of Hello, Dolly ends with the title character leading a march that bristles with her optimism for the future. The first act of this new show closes with its heroine doing the same bit in the same tempo. But the songs don't really fit the character this time around, and the new tunes aren't memorable enough to justify keeping them in the show.

With Herman's inability to cope with the property in his music, the duty falls to the authors of the book, Jerome Lawrence and Robert E. Lee. Perhaps failing to see that the songs establish the central character as a nebulous Mame-Dolly figure, they don't make an effort to help their collaborator along. As a result, they do so little that the Madwoman is not fleshed out until the second act. Nor do Lawrence and Lee establish any other character until too late. This is particularly unfortunate in the case of the villains, who are such vague "bad guys" that it's hard to know exactly what evil forces the Madwoman has to deal with.

ONLY the cast, who has the inhuman burden of providing everything Dear World's creators have omitted, cannot be blamed for the show's failure. Neither can Peter Glenville, the director, who has contributed some nice group blocking--an achievement that doesn't mean much when the stage is full of paper dolls.

Angela Lansbury, a doll who refuses to be anything but living, plays the Madwoman as if the character existed in the script and score. She nearly makes it in the first act, and in the second, she takes flight (with some help from a Herman ballad, the only song in the show that works). Frocked in costumes that look like mountains of lace and sporting a crazy carrot-colored wig, Miss Lansbury still cannot help but be beautiful. Despite the unhappy things she has to do in Dear World, you have to love her.

Most of the performers just hang around, hoping that Lawrence, Lee, or Herman might throw a bone their way. The usually redoubtable Milo O'Shea can't do a thing with the pale Sewerman, for example. And when O'Shea can't breathe life into a script, that's a sure sign the script is dead.

Indeed Dear World has failure written all over it, and all the doctoring in the world probably cannot change that. Alexander Cohen at least can be thankful that he doesn't have a flop on his hands. It's probably small consolation to him, but it's even less consolation to the audience.