George Rochberg's first opera, "The Confidence Man," which had its world premiere here Saturday night, is full of swindles and deceptions, including bogus charities, stock sales and routine betrayals of friendship. So much for the subject matter; the question plaguing critics who have flocked here for the event is whether the opera itself is also a sort of swindle.

Rochberg, a professor of music at the Univeristy of Pennsylvania, may be the archetypal composer for the Reagan era although he began adopting his new style, so conservative that it becomes radical, back during the Johnson administration. Originally a devout follower of the 12-tone system, he has decided that there is more to be said in traditional tonality, and that the Schoenberg style is useful mostly to express tension and negative emotions. The shift has made him the standard-bearer for the new lyricism in American opera and the primary target of those--once radical and now, perhaps, conservative--who believe that every major work by a living composer should be a completely new statement using a new vocabulary. In his opera, he expresses this philosophy and has some fun at the expense of his adversaries by giving mellow, romantic tunes to the good guys and chromatic or atonal music to the bad guys. The atonality reaches a high point whenever the dialogue concerns money, which is the chief point of tension in the plot.

"The Confidence Man" opens its second act in a 19th-century, Midwestern barber shop with a "no trust" sign prominently posted and an old man sitting in the corner trying to determine whether the $3 bill in his hand is counterfeit. "Down with the sign," shouts the confidence man, pointing at the notice, which violates his self-serving philosophy that people should be more trusting. The barber protests, there is an argument and the confidence man finally persuades the barber to take down the sign. Then he swindles him out of a free shave, and the scene ends with the barber indignantly putting the sign back up.

This is one of the most successful scenes in the new opera, just as a drinking song is one of the most successful musical numbers. Unfortunately, neither has anything to do with the opera's slender little plot, which is taken, expanded and otherwise altered from Chapter 40 of Herman Melville's novel, "The Confidence Man." This chapter, which probably has some overtones of Melville's life, tells the story of China Aster, a poor candlemaker who dies bankrupt because he accepted a friendly loan and optimistically tried to expand his business.

More than the story of China and his problems, the opera is a philosophical statement, heavily loaded with irony and ambiguity. One problem for the audience is that Rochberg never really resolves the ambiguities on stage, although his statements outside the work of art indicate that he believes seriously what the confidence man has proposed as part of his way of earning a living. The opera is completely a Rochberg product, with the libretto supplied by the composer's wife, Gene, and it might have been better for the final result if someone with more critical detachment had also had a hand in the process. But as it stands, as it was performed here in a very carefully prepared production by the Sante Fe Opera under conductor C. William Harwood, the opera rose above problems of structure and underlying philosophy to receive very warm applause from the capacity audience.

The staging, while it did not seem as lavish as one expects in productions of larger companies, was attractive and carefully designed to adapt a unit set to the various requirements of a prologue and 14 scenes, all set in Crystal City, a riverboat town on the Mississippi. A large, well-trained chorus with considerable personality supplied the town's people, a colorful and varied lot whose only common characteristic seemed to be their singing ability. They also supplied the composer with a convenient vehicle for some of his best tunes, and in a Rochberg opera, clearly, tunes are one of the principal things it is all about.

Baritone Brent Ellis, in the title role of the confidence man, and tenor Neil Rosensheim in the victim role of China, provided the most notable singing, with a variety of well-calculated dramatic nuances and the kind of clear diction that can make opera in English a special joy. They were ably supported by a rather large cast of solo singers and by soprano Sunny Joy Langton, who took a bit of time to warm up in the first act. Her diction was never totally clear, but she conveyed the emotion of her role as China's wife effectively.

Secondary roles were generally performed with competence and often with a fine dash of color, particularly by tenor Michael Fiacco and the basses Richard Best and Robert Osborne. There was a special problem in one role, that of The Angel of Bright Future, a character something like Mozart's Queen of the Night whom China sees in two dreams. This Angel enunciates much of the philosophy of trust and leads China to his downfall by her advice. As sung by soprano Deborah Cook, this role sounded forced, strained and ultimately false, an unpleasant effect musically although it might have been deliberately contrived by Rochberg to undermine the sense of the words being sung.

Except for occasional moments such as Cook's two arias, there was something very comfortable about most of the music in this opera. Rochberg's music has been growing more and more comfortable since the mid-1960s when he began a momentous shift of style from atonality to good, old-fashioned melody.

"The Confidence Man" may not be a masterpiece; parts of it are unnecessarily cluttered, musically and dramatically. But it is often a persuasive argument for the charms of the new conservatism, and it is calculated to give an audience comfort. The applause Saturday night indicated that it had done that. Part of the comfort is based on familiarity. The tunes, harmonies and the staging are obviously new, but not unfamiliar. They call up echoes that range from "Pagliacci" in the opening prologue to "The Music Man" in the general atmosphere and particularly in the title role.

Such elements give an audience the feeling that it is not venturing into completely unknown territory, and they are clearly appreciated. One opposite of comfort is excitement. The opera falls a bit short in that quality, but Rochberg seems to do reasonably well on the trade-off.