John Philip Sousa's "The Free Lance" was born in 1905 and practically died in Philadelphia in 1906, falling into neglect until 1979. That same city chose to revive the opera then, and that same production opened at Wolf Trap last night. With any luck, the artisty of the cast notwithstanding this production will kill the work again for another 75 years.

The story of this two-act lump is inscrutably inane, though not much worse than those of many beloved operettas. Two bankrupt neighboring kings each believe the other to be fabulously wealthy and arrange a marriage for their offspring.The prince and princess are not amused by the arrangement and run away, leaving the monarchs to find substitutes for the wedding. In a pinch, they come up with a goose girl named Griselda and Siegmund, a balding janitor to a herd of goats, he being a former free-lance mercenary warrior. That couple is already married, incidentally, but let's not bother with too many details. When the truth is found about the kingdoms' poverty, each king declares war on the other. In the meantime, Siegmund regains his hair and his strength, thanks to the sorcery of a wandering witch who turns out to be Griselda's long-lost mother. He then thinks of a way to profit from the forthcoming war. While the real prince and princess actually meet on their own and fall in love, the clever and now hairier free-lance leads troops to a two-sided victory, and amasses a good bit of property as a reward.

This nostalgic glorification of mercenary capitalism in its golden years is no operatic landmark. It is not even as clever as any Gilbert & Sullivan operetta, the genre it most resembles. Other musical associations vary, from inferior Romberg to anticipated Herbert. "Patience" came to mind more than once. Yet there were some enjoyable musical moments, including a whistled chorus and a quartet in Act One which had the definite stamp of the American musical. The melodies were generously thrown away, and while there is nothing American in itself about this stylistic potpourri, an unabashed eclecticism and vitality stood out here and there, making "The Free Lance" an unmistakable prelude to Broadway.

Directors Basil Langton and Lesley Koenig did not trust the work, which runs through tomorrow, enough to stage it faithfully. The orchestra sat stage left, their black and white uniforms clashing with the tacky decor and impeding much of the action. Stage right of the unit set usually was covered by the Iowa State University chorus, a group of strong women and almost inaudible men. The costumes varied between the Gay '90s and somewhere in the 18th century; the blocking resembled the old Mitch Miller show, and the whole business was misdirected with pushy condescension.

Fortunately the cast rescued much. John Reardon was pure joy, playing the title role with the timing of a Lucille Ball in drag. He is one of the treasures of the American stage, his many years of varied musical experience only increasing his power to own the scene with a single gesture. Theodore Uppman was a nice bit of luxurious casting as the king of Braggadocia. Evelyn Petros was the beautiful goose girl, her voice gamy at the top and lacking heft; but she can get by on the sensual gifts of her tones and looks, and she did.

The audience was in a kind and friendly mood, and perhaps there is nothing truly offensive about this opera. In a smaller theater more of the humor might have come through, and the orchestra might have been forced into the pit where it belonged. But on a first and, for many of us, last hearing, "The Free Lance" bored.