You could call it "Packing It in With P.D.Q.," or maybe "The Ultimate Bach-Buster." Because the man who came up with the "Howdy" Symphony is about to say farewell.

Or is he?"Well, it's not a goodbye to P.D.Q. Bach," says that composer's discoverer and chief promulgator, Professor Peter Schickele. "I'm going to continue to make the records for Telarc - we're already at work on a third. And I don't intend to give up the `discoveries.' P.D.Q. is, after all, the only dead composer who can be commissioned. But I've been touring for 25 years now and feel in need of some kind of a break. Maybe it would be better to call it the last tour before an indefinite sabbatical."

What it is being called, however, is "P.D.Q. Bach - the Farewell Tour," the latest installment of which comes to Symphony Hall Saturday, Jan. 26, at 8 p.m. There Schickele will once again treat Utah Symphony patrons to a madcap evening of musical mayhem with such immortal P.D.Q. Bach discoveries as the "Hindenburg" Concerto - "the original Hindenburg disaster," Schickele explains - the "Desecreation of the House" Overture and the "Canine Cantata" ("Wachet Arf!"), the last bearing the Schickele catalog number "S. K9."

The tour itself kicked off last September with a five-city run

through Australia - "my first time down there," Schickele notes - and will wind up with a concert in Pasadena, Calif., on April 1 - P.D.Q.'s birthday - with Jorge Mester on the podium. As he conducted the very first P.D.Q. Bach concert in 1959, when he and Schickele were students at Juilliard, and the first public concert in 1965, that seems appropriate.

Since then, Schickele acknowledges, not too much has changed vis-a-vis the presentations. "I still introduce the piece from the lectern, then we perform it."

What has changed, he says, is that in the early years "sometimes we had whole audiences that hadn't any idea of what to expect. That's not true now, but every now and then we still get individuals or couples who come expecting a Bach concert."

Another thing that has changed is that the orchestras themselves have become more hip to the P.D.Q. phenomenon.

"Initially we sometimes found a certain resistance on the musicians' part to do some things," Schickele says, "such as being interviewed as part of the Beethoven Fifth sportscast. But nowadays they're generally up for whatever I want to throw at them. In fact they'll even add things. In one piece there's a place where we have the oboist come up after playing a cadenza to show the conductor the cadenza is really in his part. But in one place we did it, instead of just coming up with the part, he came up and began strangling the conductor and Bill Walters, as the referee, had to separate them. So we've kept that in. It's now part of the shtick."

What is no longer part of the shtick, except on rare occasions, is the professor's habit of swinging down onto the stage via a rope from the balcony. "I've gotten too old and fat for that," he admits, adding that, at age 55, he's had to come up with new types of traditionally late and unexpected entrances.

But, he insists, neither age nor wear and tear are the reasons for calling it quits. "I just had to find more time for other projects." Over the years the P.D.Q. Bach tours have grown from three weeks to 60 concerts spread over seven months. Even with the summers off, that has left little time for such things as a couple of radio and television programs Schickele hopes to get off the ground.

Or film scores, his last major effort in that area having been the music for "Silent Running" in 1971. "The trouble with those things is they usually want you to start tomorrow," he explains, "and my life is booked so far in advance that when I want to do a movie I can't." An exception: an animated film of Maurice Sendak's "Where the Wild Things Are," for which Schickele wrote the music and did the narration. "But the only reason I had time to do that was that it was only 8 minutes long."

Then there is the serious side of Schickele, as represented by his concert music. A graduate composition student of Vincent Persichetti's, he has to his credit such things as full-scale orchestral pieces, a song cycle and a string quartet, most of which find favor with audiences and critics alike whenever they are performed.

"Certainly I hope to have more time for composing Peter Schickele music as opposed to making P.D.Q Bach discoveries," he says. He has even begun sending out a newsletter, called the Peter Schickele Rag, to apprise his fans of upcoming projects and, not incidentally, where they may obtain his recordings. (Published twice a year, it may be had by writing P.O. Box 1188, Woodstock, N.Y. 12498.)

Upcoming commissions include pieces for the Canadian Brass and Glen Ellyn Children's Chorus. He is also working, Schickele says, on a children's opera. At the same time one can almost hear the P.D.Q. bug biting.

"Just yesterday," he says, "the cellist Jerome Grossman, who is co-principal of the Met orchestra, played all six Bach unaccompanied cello suites in concert, after which he encored with P.D.Q.'s `Suite No. 1 for Cello All by Its Lonesome,' which he had commissioned." He also reflects on missed genres in the P.D.Q. canon - "I'm sure he must have written a string quartet and a violin concerto" - and, in one case, a missed opportunity.

"On the most recent P.D.Q. Bach album, `Oedipus Tex,' there is a piece called `Classical Rap,' a sort of yuppie rap song. Over the years I've gotten myself saddled with giving these pieces Schickele numbers and they've gotten harder and harder to think of. This one, for example, I ended up numbering `S. 1-2-3.' Only after it came out did I realize it what it should have been numbered - `S. thirtysomething.' "

So is this possibly not the end of the line? "Well," Schickele reflects, "as anyone who's seen me knows, I love performing and I'm not burning any bridges. I figure I can always do my `I Was Only Kidding' tour."

Kidding? That's one thing I think we can be sure of.

Seats, the Utah Symphony informs us, are available for Saturday's concert "although we expect most audience members to end up on the floor." They range in price from $15 to $27 and may be reserved by calling 533-NOTE.