Fascinating landscapes are the surest bet this week. "Niagara: Two Centuries of Changing Attitudes, 1697-1901," at the Corcoran, provides the viewer with a romantic, reverential vision of The Falls.

Also, an exhibition of photographs by the late Ansel Adams, at the National Gallery of Art. CLASSICAL MUSIC

Free concerts of the week will include: The opening of the season tonight at the National Gallery with George Manos conducting the National Gallery Orchestra; violist Cynthia Phelps, a winner of the Friday Morning Music Club Competition, this afternoon at the Phillips Collection; the Juilliard String Quartet, Thursday and Friday at the Library of Congress; the American Chamber Orchestra, Saturday afternoon at Anderson House.

Also free will be a concert at noon Friday in the New York Avenue Presbyterian Church, given by the Friday Morning Music Club, which is beginning the two-year celebration of its 100th anniversary.

Visiting singers of the week: tenor Siegfried Jerusalem, tomorrow night in the Terrace Theater, and mezzo-soprano Janet Baker, Wednesday night in the Kennedy Center Concert Hall.

World premieres of the week: Aulis Sallinen's Fifth Symphony, to be performed by the National Symphony and Mstislav Rostropovich Thursday night at the Kennedy Center; John Harbison's String Quartet, to be performed by the Cleveland Quartet Friday at the Library of Congress.

Nostalgic event of the week: a concert by the Hanover Band of London Friday night in the Departmental Auditorium, recreating part of a concert given by Beethoven on April 12, 1800. The program will include his First Symphony (which had its world premiere at that concert). DANCE

This afternoon is the last chance this season to catch the New York City Ballet's captivating "A Midsummer Night's Dream" at the Kennedy Center Opera House. The Terry Beck Troupe from Philadelphia moves into Baltimore's Theatre Project Wednesday through Sunday. Daniel West Dancers, which made its official debut last spring, establishing itself as one of the most exciting contemporary troupes in the area, appears Friday through Sunday at the Dance Place. FILM

Tomorrow and Wednesday at the American Film Institute, Greta Garbo in "Grand Hotel."

The Surrealist Cinema series Saturday at the Corcoran: films by Man Ray, Germaine Dulac and Henri d'Ursel.

Tuesday at 7:30, the Mary Pickford Theater at the Library of Congress will present the Washington premiere of Andrei Konchalovsky's "Maria's Lovers," starring Nastassja Kinski and Robert Mitchum. Thursday at 7:30, the Washington premiere of Alan Rudolph's "Songwriter," starring Willie Nelson and Kris Kristofferson.

The Soviet Cinema series Thursday at the Biograph: three Eisenstein classics -- "Strike," "Battleship Potemkin" and "Alexander Nevsky."

Among current releases, "Plenty" and, opening Friday, Martin Scorsese's vivid and imaginative "After Hours." POP MUSIC

The Patriot Center at George Mason University, Washington's newest concert venue, kicks off this week with three concerts: the Beach Boys and Three Dog Night tonight, Supertramp and the Motels on Saturday, and Howard Jones and Marshall Crenshaw a week from today.

Richard Thompson, a founding father of the folk-rock movement in England, performs at Saba on Monday.

X, one of the most progressive and provocative bands in America, performs at the Warner on Friday. THEATER

"The Foreigner," Larry Shue's wonderfully screwball comedy about dark deeds in the deep woods of Georgia, is back for a deserved return engagement (at Olney Theater). "La Cage aux Folles" is a splashy old-fashioned Broadway musical comedy with a twist for the 1980s (at the National). "Avner the Eccentric" balances silly objects on his nose, walks a slack rope and generally exerts more charm than you might suspect (at Arena's Kreeger Theater).