"How come," people ask, "the National is selling tickets for 'A Chorus Line' at $17.50 top and the cheapest seats, back of the top balcony, will be $10.50? That's more than we paid for 'Annie' and 'Hello, Dolly!'"

Two consolations spring immediately to mind.

(1) Ticket prices will be getting higher, in fact they are higher in New York.

(2) Theatergoing is not obligatory on anyone.

That one can dub such depressing facts "consolations" reflects the seriousness of the future.

Our system is based on charging what the traffic will bear. Our stage works for some years have been getting smaller and smaller. So has the potential of audiences.

Apart from the fact that only the other day I made a grocery purchase which cost 11 cents more than the same package had cost two days before, two new cost factors have slipped into theater production.

Last spring's new Equity contract, which includes per diem, for touring productions, means that the salary for even minor performers is between $600 and $700 a week. "A Chorus Line" employs 64 persons, of whom only half are visible on stage.

The second cost factor is the increasing use of television advertising. Even straight plays are beginning to use this expensive medium for getting a sell message across to the public.

Not even those who pay the bills dispute the need for performers to earn what they can while working. "I have to fight every cost I can," a producers told me recently, "but I fully understand the need for per diem road travel. In time it's going to mean we no longer can try out big productions outside New York. We need to settle in for from four to six weeks to pay off travel expenses and there just aren't that many cities where a show can stay for that long."

Having introduced a television ad to promote his "Pippin" into the second - and what became the fourth - year of its run, Stuart Ostrow the other day was saying he wished he'd slit his throat first.

"It's getting so now some shows are being predicted on what kind of TV commercial they might inspire. I know that sounds absurd, but it's true, and theater will suffer accordingly. Yes, that 'Pippin' commercial did have a tremendous effect on the show's longevity. Its cost of something like $75,000 brought in hundreds of thousands more. And TV commercials turned 'The Wiz' from a flop to a hit. But now it's getting out of hand, adding hundreds of thousands to a production budget."

New York's 88-day newspaper strike had an unexpected effect. It did not seem to harm theater ticket sales. For most of this fall, New York's theaters have been booming with progressively higher weekly grosses. While the regular critics have been missed, many had other ways of reaching their public.

But, above all, television played a stronger, if more superficial, role than ever.

It was announced that the long-running Pulitzer winner, "The Gin Game," would raise its tops to $20. That's pretty steep for a two-character, one-set play.

One reason for risking this is that "The Gin Game" has been one of the few straight plays to find a Broadway public. You charge what the traffic will bear.

The rest of Broadway has musical mania. So far 11 musicals have been announced for the season, and there will be more to come as theaters lose ambitious tenants.

Already there have been smashing flops. "King of Hearts" is not expected to last "Oh, Kay!" and "Broadway, Broadway" closed on the road before risking further losses. The Kennedy Center's Australian import, "Players" suffocated quickly, and its "Semmelweiss" died here.

One unqualified hit has been "First Monday in October," which gleaned largely slurring notices except for stars Henry Fonda and Jane Alexander. The folding of "Semmelweiss" means that "First Monday" now will move into Broadway's ANTA Theater on the more desirable west side of Times Square, not to the originally planned Lyeeum on the east. Fonda can remain only through Dec. 9, when Ralph Bellamy and Anne Baxter are likely replacements for him and Alexander.

Producers are finding ways to cut some costs.

Norman Kean's incoming musical about a Broadway musical, titled, honestly enough. "A Broadway Musical," began its testing in a church. William F. Brown's book was partially inspired by director-choreographer George Faison's experiences as choregrapher in the tryout tour of "The Wiz." The score is by Charles Strouse and Lee Adams, who did likewise for "Annie," and the cast bound for the big Lunt-Fontanne Theater includes such names as Helen Gallagher, Julius LaRosa, Gwyda DonHowe and Anne Francine. The top price will be $22.50. Producers Kean has been advertising for more backers.

Another instance of a new way to create a musical is the workshop route, which Michael Bennett more or less pioneered with "A Chorus Line." This time from a TV special, "Queen of the Stardust Ballroom," he has elaborated on "Ballroom" via workshop creation. The performers are promised a workshop fee, from $100 to $200 a week. Then rehearsals commence for four weeks at Equity's rehearsal scale, more than the workshop fee. So far "Ballroom," with Dorothy Loudon ("Annie's" first Miss Hanningan), Vincent Gardenia and Sally Jane Heit among its players, has cost, nonetheless, over $1 million and has been having a relatively unobserved tryout time at the Stratford, Conn., Shakespeare Festival Theater. Top price for this by the way: $25.

Since performers evidently exist only to perform, they seem to be going along on the workshop route idea. Several productions currently are birthing themselves in this manner, and since any work is better than no work of any kind, the players, ever optimists, are accepting this new, unheraleded system.

Making all these risks endurable is the ultimate chance that a sock success will be even more rewarding than ever in the past. Film rights for "A Chorus Line" and "Annie" come close to $10 million apiece.

The film potential for the Kennedy Center's recent musical, "Platinum," could be enormous if it manages to take root on Broadway. That Paramount Pictures is its major backer does not mean that Paramoutn will get the film rights, though it probably will have what lawyers call "first refusal." But it is meaningful that before this unusual and, I think, very promising musical, left Washington, another $200,000 had been invested for two TV commercials, a 30-second and a 60-second spot. As Madison Avenue would say, the Alexis Smith musical "has visual potential."

Finally, it is pertinent that last night's final "Hello, Dolly!" performance at the National wound up a seven-week run, which included topping even "Annie's" previous National Theater record at a lower top than "A Chorus Line" will be getting. Its advantages are that it's an upbeat, exceptionally tuneful and attractive musical with a top-flight cast and uniquely scintillating star in Carol Channing. Such a triumph is what all the others are about, but to reach a like one will take a lot more money in the future. Hand-crafting always does.