"Crossover" may be the hallmark of the performing arts of the present era. The phenomenon at any rate -- the bridging of gaps, the mingling of me'tiers -- was a conspicuously recurring motif of my recent four-day binge of performances in New York, and it didn't appear to be a coincidence.

Most of what I saw consisted of dance events; some of it would be classified as theater. And here's where the trouble starts. The borderline between dance and theater -- always, perhaps, on the fuzzy side, at least in the gray area of the avant-garde -- has grown less distinct. More and more one finds oneself repeating fundamental questions. Is this dance? Is this theater? Does it matter?

The questions themselves mushroom into a variety of areas. Performances by the Laura Dean Dancers and Musicians and the Feld Ballet prompted musings about the relationship between modern dance and ballet. "Tango Argentino" set one wondering about the viability of social dance as a stage form. Mechthild Grossmann's "Wo Meine Sonne Scheint" evenly straddled the line between dance and theater. Robert Wilson's "The Golden Windows" blended theater, mime, and visual and performance arts. The Rudy Perez Performance Ensemble raised related but different questions about the rapprochement between East Coast and West, between abstraction and literal content, between the popular and the recondite.

The questions reflect a large and apparently global movement toward the elision of boundaries among art forms. The trend toward a fusion of dance and theater is one example; the hybrid domain of performance art is another. So is what's been called "the new vaudeville," embracing elements from mime, magic, acrobatics, comedy, juggling and other popular entertainments.

The same tendency is evident within individual arts, in the erosion of distinctions between idioms, styles and genres. Just as music today may draw upon everything from classical to minimal, rock, country, blues, disco, jazz, funk, punk and heaven knows what else, so in dance the margins that separate classical ballet, say, from modern or postmodern dance, ethnic dance, ballroom dance, street dance or even ice dance are often hopelessly blurred.

Why is all this happening and to what effect? In the realm of dance, and quite possibly others as well, the motivation appears to be a quest for enrichment, a search for more voluptuous forms of expression not limited by conventional definitions of medium or territory. What we're seeing may well be a reversal of the tide of austerity that led to minimalism. Choreographers of the '60s and '70s -- by no means all, but many on the so-called cutting edge -- were bent on stripping dance down to essentials. They set out to show that dance could make do not only without narrative, or symbolic or psychological content, as Merce Cunningham had already demonstrated, but also without music, sets, costumes, makeup, fancy lighting or traditional dance habitats. Not only make do, but even profit, in trenchancy of statement.

No sooner had the point been made when the reaction set in, as if by historical necessity. By the 1980s, dramatic implication, emotional pointers and even outright stories began to creep their way back into dance composition, and as the musical public began hearing about "the new romanticism," choreographers started redeploying all the theatrical apparatus previously shunned, now further amplified by technologies like video, lasers and holography.

Minimalists became maximalists. One by one the hitherto ascetically inclined standard-bearers of post-Modernism began invading the lavish, forbidden precincts of ballet -- from Twyla Tharp, who led the way, to Laura Dean, Lucinda Childs, Senta Driver, David Gordon and others. It doesn't really alter the picture that the trek was most often made by invitation. The growth in season lengths, touring and audiences had turned a chronic shortage of ballet choreographers into a crisis of acute proportions, and the ballet companies inevitably looked beyond their own terrain for fresh creative potential. But the barefoot and sneaker people came willingly, in hopes of extending the scope of their work and reaching a more sizable public. Even an exception like Trisha Brown, who has thus far kept her distance from the ballet world, has greatly expanded the scale and texture of her pieces, in collaborations with major artists from domains other than dance.

Meanwhile, others outside the post-Modern mainstream, such as Meredith Monk, Kei Takei and Robert Wilson in this country, Pina Bausch in Germany and the Butoh school in Japan, were fashioning idiosyncratic fusions of their own that served to erase any remaining lines of division between choreographic and theatrical arts.

All this was happening, moreover, during a time when the dance world as a whole was undergoing a major gravitational shift. Throughout the postwar years until the '80s, the United States held a dominant position internationally when it came to new developments in the arts, including dance, even though some of our foremost innovators, like Cunningham and Wilson, have received far more acclaim and support abroad than at home.

But just as American manufacturing and technology can no longer claim a global monopoly in excellence, so too our dance wares are being seriously challenged by rivals from Germany (Bausch, Grossmann and others being sampled this year in the Brooklyn Academy of Music's Next Wave Festival), Japan (Sankai Juku and other Butoh groups), Latin America ("Tango Argentino"), Canada, England and France.

In many cases, the emerging creative upsurge in other nations came about as a flowering of roots planted by touring or expatriate Americans, but by now these outlanders are standing very much on their own, and in some cases -- Bausch, for one -- exerting influence on younger American artists. This is crossover of yet another kind, one that portends still more significant changes to come.

Each of the New York events I attended illuminated these propositions from a different revealing angle. In Laura Dean's case, one saw some of the potential disadvantages of crossover. Dean has expanded her choreographic palette, but at a cost. In her program for BAM's Next Wave, she introduced two new works -- "Transformer," for 11 dancers, to a two-piano score by Anthony Davis, and "Impact," for 13 dancers, to a commissioned percussion sextet by Steve Reich. Both works exhibit trademarks of her minimalist past -- spinning and repetitive geometric patterning -- to one degree or another. But both also disclose new traits, including partnering techniques, virtuosic lifts and movements plainly akin to those of academic ballet.

Obviously, Dean was reaching here for a lusher, more overtly expressive effect than was possible within the deliberate restrictions of her earlier works. "Impact" is much the more successful of the two, largely because she's on the same wavelength as Reich in her use of additive, pulsating rhythms, whereas she has trouble shaping a coherent choreographic whole to the erratically meandering Davis score, not one of his best. In both works, though, the amended movement vocabulary appears to result in a dilution, rather than a strengthening, of choreographic focus. For Dean, less was more.

Dean was a pioneer of dance minimalism. Though her background had included studies in ballet and various brands of modern dance, in the mid-'70s she went into hibernation, trying to get in touch with the primal dance impulse through solitary meditation. When she emerged, she started making extremely basic pieces based upon such elemental moves as stamping, circling and spinning. Reich was her first musical collaborator, before she began composing minimalist scores of her own. These dances had a mesmerizing power, recapturing in contemporary guise the hypnotic force of the folk rituals and trance dances that had partly been their inspiration.

Dean augmented her resources, but in limited, gradual ways. As her company and reputation grew, more ambitious projects beckoned. In 1980 she accepted the first of three ballet commissions from Robert Joffrey (the third will be realized next year), and later mounted pieces for other companies, including the Ohio Ballet and John Curry's skating troupe. The first of her Joffrey pieces, "Night," and "Burn," for the Curry company, indeed stretched her choreographic horizons while retaining the power and concentration of old.

But in "Transformer" and "Impact," the attempt to transfer a broadened choreographic gamut to her own dancers backfires. Something is lost, some kernel of purity, of intensity. The larger group of dancers she's working with now has remarkable stamina and dexterity, but it lacks the rapport of her previous ensembles. The new pieces may represent a transitional phase for Dean, as she struggles to adjust to larger canvases without losing sight of her creative center.

"Tango Argentino," aside from its intrinsic merits as a show, is also a testimonial to the robust revival of public interest in ballroom dance as an exhibitionary form -- witness as well the sellout reception for two appearances of the American Ballroom Theater in Washington earlier this year (with a third slated for Kennedy Center in February). "Tango Argentino" was the rage of Paris, where it originated; after a summer run in New York at the City Center, it returned to Broadway at the Mark Hellinger in October and is still going strong. Among its remarkable aspects is the fact that it's nothing but a string of tangos -- sung, played and danced by seven expert couples -- and yet it manages to sustain a feverish erotic pitch through number after number. Apart from the general excellence of the stagecraft, the secret lies with the fecund choreography (by Juan Carlos Copes and other dancers of the troupe) and the virility of the emotional signals the couples transmit to each other and the audience.

The crossover here is from Argentinian cafe's and dance halls to the theater, and it reconfirms the stage worthiness of social dancing that we first learned so winningly from Fred Astaire, here transmuted into a world of dark Latin passions. The dancers are of a mature age, some in their fifties or older, and it's grown-up feelings they pack into their pecking heads and whippingly interlocking arms and legs. Many of the men look like Latin versions of Jean Gabin, and the air is filled with the scent of sexual combat, even when the partners are two women or two men, as they occasionally are. As varied as the moods and moves are, by evening's end the redundancy of sound and step wears a bit thin.

At least one Washington presenter is negotiating for an engagement here. The same team that produced "Tango Argentino" now has a new property in Paris, "Black and Blue," featuring a cast of American jazz musicians and dancers, among whom is master tap stylist Jimmy Slyde. By chance, I caught Slyde at Barry Harris' Jazz Cultural Theatre the night before he left for France, his supple, rhythmically glittering feet as eloquent as the wittiest of raconteurs. As was the tango show, "Black and Blue" is penciled in for Broadway.

One of the main attractions of the Feld Ballet season at the Joyce Theater was the company's premiere of Bronislava Nijinska's historic "Les Noces," staged by the choreographer's daughter Irina Nijinska. Originally produced by Diaghilev in 1923, this extraordinary work is an early instance of crossover -- a ballet at war with most of classical dance's fundamental precepts, actually a modern dance in balletic disguise. Nijinska's repetitions, her use of massed ensembles, the percussive relation to the floor and the severe ritualism of the entire piece adumbrate the minimalism of a Laura Dean in the same way that Stravinsky's landmark score foreshadows the pulse music of Reich and Philip Glass.

The Feld Ballet's production had lots of drawbacks, including the use of taped music, cramped space, Ming Cho Lee's precious set and dancing too dainty for the weighted choreography, but the revolutionary impact of the work registered all the same. The rest of the program bore witness to Feld's own crossover impulses, as manifest in the gymnastic bravura of "Medium: Rare," his new solo for James Sewell to a Reich score, utilizing a trampoline and slanted ramps for its aerial effects; and "The Jig is Up," a typical Feld romp skillfully melding ballet technique with steps and imagery based on Irish folk dance, ebulliently set forth by a cast of 17.

Rudy Perez, a member of the original Judson Dance Theater generation and one of its most interesting thorny choreographers, transplanted himself to Los Angeles seven years ago and returned earlier this month to the Dance Theater Workshop for his first New York performance since then. He seems to have picked up some California pop veneer in the interim -- his wonderfully trim ensemble of five dancers all had designer haircuts, for one thing -- but he hasn't misplaced any of his East Coast proletarian grit or his intellectual rigor.

In three characteristically taut pieces, one an affecting memorial to Yoshiyuki Takada, the Sankai Juku dancer who fell to an accidental death earlier this year, Perez demonstrated how a choreographer of solid ideas and craft can give the common coinage of post-Modernism all kinds of arrestingly novel twists. A piece called "Debut," ostensibly a rehearsal and then a performance of a music video, abandoned its synthesizer disco midway, for, of all things, a recording of Bach's organ prelude, "Allein Gott in der Hoh" -- it's hard to think of anyone but Perez who could bring off such a coup in as choreographically compelling a manner.

Robert Wilson is the archetype of the crossover artist -- there's no medium or technique he's not apt to borrow for his wild, unclassifiable mix. "The Golden Windows," also part of the Next Wave at BAM (a planned Kennedy Center engagement fell through), is lesser Wilson in the sense of lacking an intelligible thematic spine such as those that bind together larger opuses like "Einstein on the Beach." But even minor Wilson makes other theatrical experiences seem listless and pallid by comparison. The man has the power to conjure up surreal, hallucinatory visions of such indelible aspect that once seen they're engraved forever in memory.

"The Golden Windows," a play in three acts for four characters -- the phenomenal David Warrilow was in both alternating casts -- has intriguingly eclectic music by Gavin Byars, Tania Leon and Hans Peter Kuhn (along with sound effects by the latter); costume designs by Christophe de Menil; exceptionally potent lighting by Markus Bonzli; and most tellingly of all, text, direction and design by Wilson.

Two elements stand out from the jumbled impression of the whole. One is the omniphonic play of voices, live and recorded, that seem to stream from all points in the auditorium, bringing words that are a collage of enigmatic phrases. The other is the visual side of the piece -- a corner of Earth suspended in a foreboding night sky, a mysteriously radiant doorway, a man hanging by a noose and conversing with himself in changing voices, a staggeringly vivid earthquake, a spooky meteor shower. No Houdini ever had magic to outdo this.

"Wo Meine Sonne Scheint" (translated as "Where My Sun Shines for Me") boasts Mechthild Grossmann's far more modest but no less virtuosic solo performance of a piece devised by her and Helmut Schaefer, another entry in this year's Next Wave. Actress-dancer Grossmann has been one of Pina Bausch's collaborators and performers since 1976; she's also worked with numbers of other theater and film directors including the late Rainer Werner Fassbinder.

With striking features and a husky voice suggesting a Germanic Tallulah Bankhead, she has a prepossessing stage presence. But more than that, she has such thorough command of her physique, both in pose and movement, that she can make her body speak as articulately as her voice, and it's this combination of dance and acting prowess that gives her characterizations such resonance. The piece is an exploration of the cliche's of male-female relationships -- at one point Grossmann transforms herself with comical brilliance into your stereotypical slovenly, macho male specimen, to make her points, so to speak, from the other side of the fence.

Perhaps the oddest, most unexpected and poignant instance of crossover I encountered on this trip was none of the above, but Jean-Luc Godard's controversial film "Hail Mary."

What an irony in its condemnation by church authorities, demonstrators and now its Boston exhibitor. Here is Godard, the one-time polemic Maoist radical, retelling the story of the Virgin Birth from a modern standpoint, as a meditation on the eternal war of the flesh and the spirit, and the miracle of creation. It's not only the most beautiful motion picture I can recall seeing in at least a decade (photography by Jean-Bernard Menoud and Jacques Firmann), and the most inspired in its conjunction of sound and image (Godard uses wisps of Dvora'k and Bach to turn up the emotional flame in strategic passages), it also turns out to be as quintessentially pious a work of film art as anyone could name.