Circusgoers may detect little difference this year in the music accompanying elephants, trapeze artists and other performers, but a labor dispute has touched off some sour notes behind the scenes.

The dispute concerns whether the trumpets, tubas or other instruments are tooted by local or imported talent.

Traditionally, the Ringling Brothers and Barnum & Bailey Circus management has contracted for local musicians in each city on the tour. This year, however, management has arranged with Cas-Pet Musical Contractors, Inc., for troupes from city to city.

The American Federation of Musicians, AFL-CIO, whose members used to provide the indigenous talent here and in other cities, is unhappy with the change.

"please don't patronize Ringling Brothers Circus," requested an advertisement placed in yesterday's Washington Post by the D.C. Federation of Musicians, Local 161-710 of the AFM

Sam Jack Kaufman, longtime president of the local, said union representatives would be handling our literature pleading their case when the circus opens its run at the D.C. Armory today. Inside the armory, Caspet musicians are expected to be providing the marches, waltzes and fanfares.

Which mucisians will serenade audiences at the Capital Centre, where the circus opens a second run April 20, is still up in the air.Kaufman said the union had a contract with the arena's management for supplying musicians there.

Jerry Sowalsky, a Ringling Brothers attorney, said circus officials were "examining" that pact. He said the Capital Center situation was "still a fluid one."

Sowalsky said Ringling Brother's contract with Cas-Pet for full-time traveling musicians was designed to assure more uniform musical quality at a one reasonable cost.

"They'll tell you that quality was deteriorating, said Kaufman. "That's a lot of baloney. If anything, our musicians are getting better."