Contrasting spectacles: at Radio City - and the Public Theater.

The Magnificent Christmas Spectacular Conceived, produced, and directed by Robert P. Jani. Starring the Rockettes.

Radio City Music Hall is up and away with its annual Christmas extravaganza, spreading joy and good cheer, sweetness and light, veneration and general jollity. The celebration, which premiered in 1979, varies only in details from year to year. Why change, when you've got a good thing going?

Music Hall aficionados will notice that the 1984 ''Magnificent Christmas Spectacular'' adds a Rockettes kick routine to the beginning of the show. According to the management, this marks ''the first time they will perform one of their precision dances for Christmas audiences.'' But that's not all. The 36 superbly synchronized ladies also provide the semifinal climax of the program with the dazzling drill of ''the Parade of the Wooden Soldiers.'' The rockettes seem to time everything, even the applause that greets their breathtaking stage crosses. And anyone who has watched the long, thin line of toy soldiers gradually topple has witnessed the domino theory in action.

The 12-scene spectacular mingles traditional and newly minted melodies. Among others, the choristers raise their voices in ''Oh Tannenbaum,'' a favorite on the German Christmas hit parade long before it served Civil War America as the tune for ''Maryland, My Maryland.'' Nicholas F. Jani and his colleagues present their own versions of ''The Nutcracker'' (Tchaikovsky) and the happy ending of ''A Christmas Carol'' (Dickens).

''The Traditions of Santa Claus,'' illustrated with large-scale projections of Saint Nick, leads into Tom Bahler's setting for Dr. Clement C. Moore's 1822 ''A Visit From St. Nicholas,'' replete with Santa sleighing off into the stars, drawn by his faithful reindeer. The show takes a global excursion with folk songs, carols, and dances from all the hemispheres and both sides of the Iron Curtain. The Music Hall knows no impediment to detente. Christmas round the world is followed by a respectful acknowledgment of Hanukkah and the Jews' sacred festival of lights.

A program note for ''Twelve Days of Christmas'' informs that it has been arranged and programmed and is performed by Don Dorsey on the Prophet V and Synclavier II digital Synthesizer. All of which seems to have inspired the dancers to a particularly jaunty performance. It's a hard act to follow. But the swingy New Yorkers manage the feat handily with their Christmas medley. Here, as elsewhere, the show's large cast of singers and dancers receives solid support from the orchestra led by music director-conductor Joseph Klein.

Traditional carols as well as biblical and other texts (beautifully spoken by John Cunningham) accompany ''The Living Nativity,'' the pictorial manger scene that closes the performance. Notwithstanding its theatrical aura - with camels, sheep, and donkeys for atmosphere - the scene achieves a degree of reverence appropriate to the solemnity of the sacred event.

Above all, of course, ''The Magnificent Christmas Spectacular'' is just that, a showmanly marshaling of talents and stage effects at what used to be called ''the showplace of the nation.'' Christmas, as they say, comes but once a year and nobody celebrates it quite like the Music Hall.

The Ballad of Soapy Smith, Play By Peter Parnell. Directed by Sheldon Larry.

In the theatrical hyperbole of its 1890s era, ''The Ballad of Soapy Smith'' would probably have been described as a mighty dramatic spectacle - with shootings, a hanging, military parades, displays of Old Glory, and pianistic renditions of popular refrains. The description would not have been amiss. All this and more fills the stage and spills over into the auditorium of the Public/Newman Theater as Michael Weller traces the rise and fall of Jefferson Randolph (Soapy) Smith, con man extraordinary.

Producer Joseph Papp and the New York Shakespeare Festival have commemorated Soapy's exploits in Skagway, Alaska, with a populous and colorful staging. The performance projects the audacity of the man and simulates the rambunctiousness of a lawless frontier milieu at the time of the gold rush. From the moment Soapy (Denis Arndt) and his partner George Wilder (Jon DeVries) approach their landing in a fogbound rowboat until the fateful denouement, the adventure tale pursues a time-honored course.

Versified Paul Andrew MacAleer (Christopher Cooper) doubles as rhyming commentator and participant in the events. Between them, playwright and balladeer tell how Soapy - ''the king of the Denver 'Sharpers' '' - after disposing of a rival, organizes his cadre of fellow con men and manipulates obliging members of a Skagway ''law and order'' vigilance committee. While extorting money for the protection of vice, Soapy reduces violence in the community. At the same time, he earns the status of local hero with civic-minded , patriotic benefactions.

When honest town engineer Frank Reid (Kevin Tighe) finally comes to terms with Soapy, it appears that the rascal has truly soft-soaped Skagway. The con man has overreached. Instead of enjoying the reputation, power, and respectability so cunningly pursued, he is betrayed into a fatal showdown.

Mr. Weller cleverly applies a contemporary perspective to melodramatic devices from the era of the play's events. On the whole, the mingling works. However, at 23/4 hours (with intermissions), ''The Ballad of Soapy Smith'' risks overextending itself, or at least indulging in an excess of incidental details and local color.

On the positive side, the performance fulfills the play's theatricalism. Imaginatively staged by Robert Egan, who developed and directed the original Seattle Repertory Theatre production, ''The Ballad of Soapy Smith'' amalgamates authentic social history, fictionalized folklore, and spectacle.

As Soapy, Mr. Arndt brilliantly personifies the charm and shrewdness of the silver-tongued Southerner for whom gulling the citizenry is as natural as breathing. Mr. Arndt endows the ruthless rascal with a guile calculated to hoodwink the sternest skeptic. Besides those already mentioned, principal members of a huge and excellent cast include Pierre Epstein as an easily duped local minister and Cherry Jones as the minister's more perceptive niece.

Eugene Lee's scenery has the ramshackle look of a frontier town under rapid construction and reconstruction. The trunkfuls of period costumes are by Robert Blackman. Jennifer Tipton lighted the scene. Besides some incidental songs by Mr. Weller, the music consists of popular airs of the '90s, performed con brio by pianist Nancy Waldman.

Haarlem Nocturne, ''Theatrical concert'' conceived by Andre De Shields. Written and directed by Mr. De Shields and Murray Horwitz. Starring Mr. De Shields.

After mixed fortunes as the Princess, a small legiti

mate theater, the renovated Latin Quarter has reverted to its most famous name and reopened as a cabaret in the modern manner. That is to say, the tables are tiny, the chairs hard, and the overcrowding allows just enough room for patrons to applaud. Applaud they did as Andre De Shields and fellow entertainers launched a new era for a new-old spot with ''Haarlem Nocturne.''

In addition to its Dutch connotations, the double-a in ''Haarlem'' signals something rather special about what the versatile Mr. De Shields describes as a ''theatrical concert.'' Among other things, it's probably the hottest concert in town. After a lengthy warm-up at Off Broadway's La Mama, the syncopated nocturne proves to be a ne plus ultra of nightclub revues. The show mixes rock, blues, gospel, cool jazz, '60s hits, and original songs (several of the last-mentioned written by Mr. De Shields). The entertainment is smart, hip, and stylish. It is also hokey, jokey, and smoky.

A loose scenario connects the opening selections in which Mr. De Shields, who favors blazing red costumery, experiences the highs and lows of a black New Yorker. With a flashback glimpse at slave origins, the protagonist revels in the Big Apple and then discovers that the party's over. Suitcase in hand, down but by no means out, he retreats up the ramp of the seating section and yields the stage to a female trio.

Here as elsewhere, impresario De Shields displays his confident willingness to share the scene with his exceptionally talented fellow artists. Among other numbers, ''Secret Love'' features Debra Byrd, ''Say It Again'' gives the lead to Freida Williams, while ''Hit the Road Jack'' and ''Waterfaucet Blues'' enjoys memorable vocalizing by Ellia English. When Miss English appears atop a staircase in a purple dress and a mood to match, she provides one of those moments that wow the customers. choAnd ''Haarlem Nocturne'' has more in store. For examples there are Mr. De Shields's wickedly funny ''Bad Boy'' and the innocently charming ''Mary Mack,'' a traditional children's song set to this nocturne's beat.

''Harlem Nocturne'' was co-written and co-directed by Murray Horwitz. The performance owes much of its verve to the combo led by music director-orchestrator-arranger-pianist and sometimes performer, the indispensable Marc Shaiman. The production was designed by David Chapman (setting), Bruce C. Edwards (costumes), and Marc B. Weiss (lighting). The Latin Quarter has reopened with a sophisticated divertissement featuring a bouquet of black talent presented in a snazzy New York manner.