In Italy, where opera is treated as a blood sport, tenors must perform like star athletes or risk the kind of booing that would make an American opera lover blanch. Like athletes, they're expected to use the slenderest of physical resources to overcome nature and produce superhuman feats of skill -- on a daily basis. Also like athletes, they're rewarded with throngs of cheering fans, smitten women, determined paparazzi and clamoring producers. The real superstars command fees that could fund a small country.

The so-called Three Tenors -- Luciano Pavarotti, Placido Domingo and Jose Carreras -- have taken the genre to Olympic heights, and have done so for an incredibly long time. Their fame has spread well beyond the usual opera-listening demographic, and the Three Tenors moniker has exponentially expanded both their celebrity status and their wallets. But now, as all three are facing retirement, speculation is rife as to who, among the world's current crop of tenors, could step into superstardom as the "Fourth Tenor" (or, indeed, the Fifth or Sixth).

Fine singers such as Marcello Giordani, Jerry Hadley, Ben Heppner, Vincenzo La Scola and Richard Leech have failed -- through vocal inconsistency, the simple fact of aging or lack of the necessary charisma -- to generate the audience frenzy or attract the media attention to make any of them the genre-busting Next Big Thing. Currently the fast track to Fourth-Tenordom is populated by a group of photogenic young singers with exciting voices and musical smarts to match, including Roberto Alagna, Marcello Alvarez, Jose Cura, Salvatore Licitra and Ramon Vargas. But recently a slew of promising young tenors have thrown their hats into the ring, with debuts at major opera houses and tantalizing new recital discs.

Perhaps the most prodigiously gifted of the new group is Juan Diego Florez. His voice -- light, bright and tightly focused, its hint of nasality never compromising a fundamentally sweet tone -- is tailor-made for the florid runs and ornaments of the early-19th-century bel canto repertoire. There are plenty of showpieces by Rossini and Donizetti to be enjoyed on his "Great Tenor Arias" CD (Decca) -- perhaps too many for a single sitting, as even a superlative voice like his can weary a listener who's put through such rigorous paces aria after aria. Verdi and Puccini selections offer brief respites from the fusillade of notes, but his voice isn't ideally weighted for those composers, and his readings of them sound a bit faceless and insubstantial.

Of course Verdi and Puccini are the Three Tenors' meat and potatoes, and any singers seeking Tenors audience share should be able to sink their teeth into such hearty Romantic fare without hesitation. Joseph Calleja does just that on his "Tenor Arias" recital (Decca), lavishing the music with a melting beauty that brings to mind the great Beniamino Gigli, and the kind of soft, honey-toned phrasing that was Ferruccio Tagliavini's trademark. Much of Calleja's artistry, in fact, harks back to a nearly lost old-school tradition -- not least his manner of suggesting emotion through careful dynamic shadings of the vocal line rather than through overt histrionics, and the quick vibrato that lends his tone a distinctive "fluttering" texture. That rapid vibrato -- which was common in singers three or four generations ago but is rare today -- is, remarkably, present in all four of the new voices under consideration here but is most pronounced in Calleja's. It makes his a unique sound, and it takes some getting used to.

Calleja's potential Achilles' heel is his high notes, which sound less colorful and secure than the rest of what he sings. And that's just where Rolando Villazon scores so conspicuously on "Italian Opera Arias" (Virgin Classics). Here is a virile, ringing, full-bodied voice, top to bottom, with a certain baritonal heft and a hint of a sob in the phrasing that really sells a good Italian tune. He's more emotionally demonstrative than Calleja but never to a shameless or grandstanding degree. Where Calleja, for example, shows us Edgardo's sensitive soul in the final scene of Donizetti's "Lucia di Lammermoor," Villazon reveals the heroic lover. The extra weight in his voice also allows Villazon to balance bel canto with the aptly nicknamed "can belto" tradition: the early-20th-century verismo of Puccini and Mascagni.

But to hear big, beefy, heart-on-the-sleeve verismo arias sung by a clarion, no-holds-barred tenor, you'll have to try the CD "Opera Arias" (EMI) from Yu Qiang Dai, the Asian-trained, Beijing-based tenor who has made it his mission to bring Italian opera to the provinces of China. You might assume his grasp of the idiom to be superficial at best. And you'd be wrong. Yu Qiang Dai has thoroughly absorbed the style of burnished, trumpet-toned singing that's seldom been heard since the days of Mario Del Monaco and Franco Corelli. (He's even inherited Corelli's lisp!) And if he could occasionally be accused of shamelessness and grandstanding, that solid bronze voice, and ability to milk Italianate passion from every phrase, could win anybody over.

Now if this were a horse race (and among opera fanatics, isn't it always?) my money would be on Villazon as the tenor du jour who could go head to head with the big boys and find a crossover audience. But what about that ultimate crossover star -- the poster boy for "pop opera" -- Andrea Bocelli? The blind Italian crooner has recently been recording complete operas (at a time when record companies have almost entirely eliminated such "extravagances"), in an effort to be taken seriously as a legit opera singer. The early results revealed a lovely but largely unsupported voice, with short-breathed phrasing and feathery high notes. But a new recording of Verdi's "Il Trovatore" (Decca) tells a different story. Bocelli's voice now sounds as if it's been cut from a single cloth, the tone darker and more robust, the phrasing more fluid, the high notes thrillingly punchy.

But is this how Bocelli sounds in the flesh? Reports of his fledgling appearances in fully staged opera suggested a slight voice that barely made it past the footlights at certain points. No doubt he's been working hard over the last few years to master proper operatic vocal technique. No doubt, either, that this pop-savvy, mike-reliant singer has had his vocal presence beefed up in the studio. Of course, who's to say how much electronic enhancement is at work on any of the discs at hand: Florez's small-scale voice has been made very prominent in the mix, to take one example, and Yu Qiang Dai has had substantial reverb laid over his. But Bocelli often seems to be in a different acoustic environment from the rest of the cast, with volume that leaps past his accustomed lyric sound to suggest, at certain points, a full-scale dramatic tenor. Those who truly love this blood-and-thunder Verdi tune-fest, however, might give this "Trovatore" a skip, especially as the studio cast assembled is, at best, of the solid, second-tier variety.

There's nothing second tier about Carlo Bergonzi. In fact, anyone who cares about the art of great singing should hear the reissued three-disc collection "Verdi Arias" (Phillips), recorded by the legendary tenor in 1974. Bergonzi was hardly a matinee idol -- with his diminutive stature, knobby features and avuncular paunch, he looked more like the neighborhood butcher than, say, the dashing Duke of Mantua. But listen to the vivid character he creates in the duke's three arias from "Rigoletto," through a complete, idiomatic ownership of the words and an elegant, naturally communicative ease with the musical line. ("La Donna e Mobile" is far more detailed in expression here than the renditions on any of the recent recital discs.) And that command is in evidence throughout the selections in the set, which cover all the tenor arias Verdi wrote for his stage works.

One could argue that Bergonzi's voice is too ample for Fenton in "Falstaff," and too lyrical for the title role in "Otello," but thanks to his intelligence and wholehearted commitment -- not to mention the unfailing vibrancy of his timbre -- the music from those operas sounds just as right for him as his more accustomed repertoire. One word of caution: High-note fanciers will have to endure a degree of strain and flatting in the most stratospheric regions. These recordings were made a good decade and a half after Bergonzi's prime. But while his records from the late '50s and early '60s may find him in fresher vocal estate, this comprehensive collection of popular and rarely heard selections is an unmatchable primer in the art of singing Verdi.

Listening to Bergonzi provides a useful reminder that the Three Tenors are only a handful of the great vocal athletes who've thrilled fans of Italian opera over the past two centuries. The ground seems to be thick right now with tenors who can leap higher, run faster and throw farther than their competition. If we're lucky, a new Bergonzi might emerge from the pack -- a true artist among athletes.