ROME - Monica Castro was crying on the edge of the stage, not because Hair was leaving town but because it is so beautiful.

"I've been singing that finale for three months and I still cry every time" she said.  "It is so beautiful, those words, about letting the sun come in."

The 81st and almost the last performance of the Rome production of Hair had just ended on the stage of the Sistina Theater.  Six people from the audience of - well, the producer said 1,000, and why argue? - had lingered to praise the cast.

Five days later they took to the road to see if they could find any enthusiasm somewhere else in Italy. Rome audiences had been dead.

"And it's been that way every night" Franco Cancellieri, the producer, complained.

It was intermission and he was sitting in front of a bigger than life picture of a drop-out from the nude scene.

"We have averaged 1,000 persons a day since we opened September 3, which means we have played to 55,000 or 65,000."

But it is still not fun to have produced the shortest run in Hair history.  Sort of like a crew cut.

"I haven't made back my investment.  But I think I can keep the show going for a year.  Maybe, maybe I'll make it back."

Cancellieri has already put together a tour of long and short runs and a nightclub stand that will keep the cast of 29 busy through most of February.  There will be a one night go in san Marino, three weeks in Bologna, two months in Milan, and a week in the huge La Bussola night club during the carnival at Viareggio.

"And I hope to go also to Turin and Florence and to the south, to Naples, maybe to Sicily.  And I hope we can come back to Rome next summer with a more popular version.  If I can't find a place like the Teatro Brancaccia maybe I can rent a circus tent."

The top ticket price for seats has been $8, but that's not the only commercialism.  The programs peddled for $3.20.  And the audience was captive before the opening act and intermission for the projection of commercials in living color on a giant movie screen - ads for such diversion as deodorant soap, digestive liqueurs and house odor sprays.

The production is bright, colorful, with all but one song in Italian, fairly topical in terms of Italian jokes and references, and very professional.

So nobody is quite sure why it failed.

The most common explanation is that Romans are Romans and they have killed theater in this city almost as effectively as they did Julius Caesar.

"I really think it was terribly good" a woman from Florence - and therefore innocent of the Roman reputation - commented.  She had seen Hair in Paris and found the Roman version a pale second.

But others who had seen productions elsewhere didn't agree with this criticism.

"I think there are four explanations for the failure." a Roman professor who loved the show theorized.

"First of all it is not new.  Everybody here had heard the music and had heard about the show for a long time.  Then, some of the content - even in the Italian production - dealing with Vietnam and other issues, was just too American.  Italians don't care about anything outside Italy.  In the third place, Romans are apathetic.  And, something even worse, there are some people who think it is chic not to show any response in the theater, which could explain why some people never bothered to clap."

The nude scene was as naked as any other hair production, meaning totally, even if the cast assumed postures of children in the Garden of Eden who had just had their first bite of the old apple.  So much flesh had not been displayed here since the last mass dunk in the Baths of Caracalla.

And the , shall we say, cross fertilization of organized religion and such subjects as masturbation certainly set precedents undreamed of when Mussolini gave the Catholic Church extraordinary powers in the Lateran Pacts of 1929.

"I was invited opening night but I stayed away" one Roman confided.  "I just didn't know what the police might do."

They did nothing.

"Opening night was a real honor." one cast member recalled...

"All the big names of Italian cinema and society were here and the photographers kept pushing us to one side so we wouldn't get in the way of pictures of Marcello Mastroianni."

"There was an opening night dinner but we weren't invited, just the celebrities in the audience" an actress said.

No one on stage seemed clear why the young man who interrupted the producer had no money.

"We've been getting paid.  Franco held up the record royalties once but when we threatened not to go on he gave us the money."

The real love of the cast is Victor Spinetti, the British actor and director who directed the show.  He welded remarkable spirit in the troupe, carefully breaking down the Italian tradition of "bella figura", the preoccupation with appearances and status, with the help of an international cast.

It's the same spirit that prevailed all through the run, even when the audience was sitting on its hands.  Enough to make a girl cry regardless of what the lyrics say.