CLASSICAL MUSIC

Nobody should have any trouble finding a music festival this week in Washington with a guitar festival opening Tuesday at the University of Maryland, a harpsichord festival running Thursday through next Sunday at the Library of Congress, the Smithsonian and Mount Vernon College, the Summer Chamber Music Festival opening Tuesday night at the Library of Congress, a one-pianist-per-week piano festival at the National Gallery, and a minifestival of operas at Wolf Trap.

The New York City Opera opens its brief Wolf Trap season Tuesday with "Carmen," to be followed by "La Bohe me" (opening on Wednesday) and "Die Fledermaus," opening on Saturday. The programming is less daring than it has been in some past seasons, but it would be hard to find three operas more calculated to appeal to the kind of large audience that Wolf Trap attracts.

Music of composers who are members of the Friday Morning Music Club will be featured tomorrow night in a concert at Strathmore Hall, Rockville.

The Sixth Annual Conclave of the Southeastern Historical Keyboard Society (June 12-15) will be highlighted by two harpsichord competitions, for composers and performers, as well as several concerts. Anthony Newman and George Lucktenberg will premiere several new works Thursday night at the Library of Congress,and Kenneth Gilbert will give a recital Saturday night at the Smithsonian.

Also worth noting: Songs of Mendelssohn, Schumann and Mahler performed by mezzo-soprano Mary Pat Finucane and baritone Lewis Freeman, Friday night at the New York Avenue Presbyterian Church; pianist Mary Kathleen Ernst, tonight at the National Gallery; the Euterpe Chamber Players, tonight at the Reston Community Center; pianist Josef Tapia, tonight at Strathmore Hall.

DANCE

The Stuttgart Ballet presents the final performance of its current visit to the Kennedy Center this afternoon, featuring "Les Sylphides," "Canto Vital" and "Gaite' Parisienne." Two concluding performances of "Visiting Hours," the latest dance-theater work by Wendy Woodson and Achim Nowak, will be given by their troupe, Present Company Inc., at New Playwrights' Theatre this afternoon and evening. At the New Dance Place in Brookland, the D.C. Contemporary Dance Theater this afternoon opens a free summer series of performances and discussions by Washington area dance troupes. Sankai Juku, the internationally renowned Buto dance company from Japan, returns to the Warner Theatre Thursday through Saturday evenings with the Washington premiere of its 90-minute symbolic epic, "Jomon Sho."

FILM

The Joseph Mankiewicz retrospective continues at the American Film Institute tomorrow and Tuesday with "A Letter to Three Wives," as close as the cinema will ever get to a Cheever story. All week, the "Hollywood: Legend and Reality" series continues with such classics as "Swing Time," "The Maltese Falcon" and, tonight, Preston Sturges' remarkable comedy, "Sullivan's Travels."

Wednesday at 7:30 at the Smithsonian's Carmichael Auditorium, David Lean's epic, "Lawrence of Arabia."

Next weekend at the Biograph, "Sugarbaby" in a double bill with "When Father Was Away on Business," two of last year's best foreign films.

The "Real Life America" series continues at the Library of Congress' Mary Pickford Theater Wednesday with Frederick Wiseman's "Welfare."

The National Theatre's free summer cinema series kicks off tomorrow night at 7 p.m. with "Flying Down to Rio," starring Fred Astaire and Ginger Rogers. .

Tuesday and Wednesday at the Biograph, two exquisite actresses in a double bill: Jessica Lange in "Sweet Dreams" and Sissy Spacek in "Coal Miner's Daughter."

Among current releases . . . you've got to be kidding.

POP MUSIC

The watchword this week is BIG:

On Tuesday, it's the Crosstown Charity Jam, with Washington musicians and clubs contributing their services and raising funds for more than a dozen local charities and nonprofit organizations. The participating clubs are Babes, Bayou, Birchmere, Blues Alley, Chapter III, Chelsea's, Kilimanjaro's, Roxy and 9:30.

On Saturday, it's a classic r&b and soul blowout at RFK Stadium. Patti LaBelle is the headline, followed closely by Maze, Freddie Jackson, New Edition and Ashford and Simpson, with newcomers Ready for the World, Cherelle, Colonel Abrams and Alexander O'Neal bringing up the rear. Needless to say, it's an all-day affair.