It's a measure of the staying power of the Joffrey Ballet that the four-day engagement the company initiated at the Filene Center last night marked the start of the troupe's 10th anniversary season at Wolf Trap. Wolf Trap is also 10 years old this summer, and the Joffrey is one of the few visiting attractions that hasn't missed a summer here.

In the course of the decade, the company has seen many changes, but its basic character has remained much the same -- a combination of populist veneer with a venturesome, broadly eclectic repertoire. Though last night's house seemed smaller than those for previous years' openings, it was no less volubly enthusiastic. The company pays a certain price for its hard-earned popularity, though, in stylistic dilution and homogenized personaltiy. Both sides of the Joffrey coin were in clear view last night -- the youthful effervescence that underlies the troupe's democratic appeal, and the bland, billboard streak that appears to be its corollary.

Of the five programs the company will present during the current visit, last night's was the least prepossessing, including only one strong local premiere -- Jiri Kylian's "Return to the Strange Land" -- along with a muted revival of Ruthanna Boris' "Cakewalk" and two of the obligatory stock of ballets by the troupe's associate director, Gerald Arpino ("Suite Saint-Saens" and "Fanfarita").

Kylian -- whose own company, the Netherlands Dance Theatre, will be appearing at Wolf Trap next week -- is one of the most interesting young choreographers on the international scene. His style of dance rhetoric, with its seamless curvature and sweeping convolutions, is as distinctive as a monogram. It also, however, courts the danger of self-limitation: the "Kylian look" tends to smother the differences between one work and the next. "Return," created for the Stuttgart Ballet in 1975 as a memorial to John Cranko and set to music by Leos Janacek, is a fairly pungent and characteristic example of the Kylian manner. The stark agadio duet and the sculptural finale which follows are the two most compelling sections, and they abound in the kind of fluent unwindings which are the choreographer's trademarks. But the Joffrey cast lacked intensity, and the work's pathos, perhaps for this reason, looked rather synthetic.

Even so, Kylian's rapturous imagery was the most potent stuff of the evening. "Cakewalk" retains its lilt and comic charm as a ballet (the Gottschalk-Kay score is hard to resist), but last night's dancers demonstrated neither the parodistic bite nor the virtuosity to do it full justice. The monotonously manic "Suite Santi Saens" and the hokey "fanfarita," with Luis Fuente strutting around like a Flamenco Elvis Presley, lent high energy to the program's first half, but not much else.