The world-famous Vienna Volksoper is on the last leg of its first-ever United States tour (at the Kennedy Center in Washington through next Sunday). The trip has not been altogether auspicious for the troupe. The ''Fledermaus'' and ''Merry Widow'' were generally drubbed by critics. But the new production of Kalman's ''Czardas Princess'' - seen only in New York and Washington - was an unqualified artistic hit. Here in the Big Apple it was the only sellout, though the work itself is little known in this country. The production was stylish, and deftly cast. The outstanding performance in that show was the Boni of Jack Poppell.
The authority and naturalness with which Poppell managed everything from dialogue to dancing bespoke a born-and-bred European. I was therefore surprised to discover that Mr. Poppell is a young American. It is rare for Americans to find a permanent place at the Volksoper - an institution where one has to talk, sing, and generally think on one's feet in impeccable German.
The closest pigeonhole possible to describe Poppell's abilities is that of the traditional song-and-dance man in the Broadway theater. With a light tenor voice, charm to spare, and a suave dancing presence, he has been declared a find by many critics here.
I had a chance to talk to Mr. Poppell while the troupe was in New York and asked him how it was that he landed in Vienna. ''I've always been pretty adventurous,'' he replied. ''I studied piano very intensively when I was small.'' His last piano teacher was also a voice teacher, who had a dream that one of her students would eventually study at the hallowed Mozarteum in Salzburg. This might seem feasible for a city boy, but Mr. Poppell lived in Pensacola, Fla., where he heard his first ''opera,'' Offenbach's frothy ''La Perichole.'' He happened to be a member of a fine chamber choir that was sent to Salzburg to take part in the Festival of Three Cities.
Instead of a graduation present, he asked his parents for the money to enroll in the three-week summer program at the Mozarteum. His teacher there was the renowned coloratura soprano Erna Berger, who, after initially turning him down, worked with him every day for three weeks. ''She was wonderful to me. I came in 18 years old, and had a voice about, well . . . we won't talk about that.'' At the end of the three weeks, Miss Berger asked Mr. Poppell if he really wanted to pursue a vocal career. She said, in his words, ''There are definitely vocal limitations, but I think you've got the musicality and the drive to do it.''
He was able to get an audition for the coming semester at the Mozarteum, found a teacher, and completed the five-year course there. From Salzburg, it was on to the opera at Lucerne, Switzerland, for 130 performances in 13 roles. He then joined the opera company in Oldenburg, West Germany, and suddenly had a successful audition at the Volksoper.
''For me, it's been just a wonderful experience. I had the great good luck to slide into the first position in my Fach (loosely translated as voice type).'' And on the basis of that audition, Robert Herzl, who was planning the new production of ''Czardas Princess,'' designated Poppell as Boni - to great initial resistance.
''Everyone said, 'It can't work (using young singers in all these roles).' The previous production had been legendary. These people (the Volksoper stars) - I don't think you can imagine in New York what kind of stars they are. They're worshiped. The people come when their name is on the cast - it doesn't matter what they're doing, the house is full. So we were up against a lot - the whole new cast.''
The American dates mark the tenor's US professional debut. I asked him what it was like, stepping out onto the New York State Theater stage (an auditorium that seats more than 2,600) after the 1,400-seat intimacy of the Vienna stage. ''We had a rehearsal on the day of the opening, and I walked out on stage and saw that auditorium and thought, 'Oh no, I'm going back to Vienna right quick!' I was really scared. (Fortunately) my nerves are good when I'm on stage, and I felt secure. And the audience was really wonderful.''
Poppell freely admits that he could spend his life at the Volksoper, ''if the contract is right.'' In the future he would expect to have more of a say in the roles, he frequency of performances, and the liberty to guest-perform around Europe. He even thinks he might be able to do the Viennese comic roles one day - something few foreigners can manage because the dialect is so difficult to master. ''In another two or three years, if the success keeps growing as it has done in the past two seasons, then the Viennese won't mind. They'll forgive me for not being able to (say things with the right accent).''