Without a doubt, the most important event in classical music this week is the opening of the Baltimore Symphony Orchestra's season. It will be the occasion of the official installation of Marin Alsop as the group's music director, the first woman to hold that position with a major American symphony orchestra. A celebrated champion of contemporary music, particularly by American composers, Maestra Alsop has come into her new job with a full head of steam, putting together a more exciting program of concerts for this season than we have seen from either of the Washington-Baltimore area's major orchestras in years. Those who attend one of her four opening weekend appearances will be witnessing history in the making.

KEEP IT CONTEMPORARY:
>> Alsop's program this weekend is a daring combination of Gustav Mahler's bombastic yet dancing Fifth Symphony with Fearful Symmetries by neo-Romantic minimalist John Adams (from 1988, with synthesizer and saxophone quartet). The absolute premiere will be on Thursday when the BSO opens the season here at Strathmore (September 27, 8 p.m.), for which a few tickets remain at the time of writing. The group will also give three performances at Meyerhoff Symphony Hall in Baltimore, on Friday (September 28, 8 p.m.), Saturday (September 29, 8 p.m.), and Sunday (September 30, 3 p.m.).

>> If you know nothing about Adams or Fearful Symmetries, hear about it directly from the source. John Adams will inaugurate the new Composers in Conversation series sponsored by the BSO, when he appears on Wednesday (September 26, 7:30 p.m.) at Baltimore Theater Project. That means two trips up to Baltimore this week. Tickets: $10.

>> The striking young mezzo-soprano Sasha Cooke will give the opening recital of the Young Concert Artists Series on Sunday (September 30, 2 p.m.) in the Kennedy Center Terrace Theater. Judging by her luscious voice and engaging stage presence at Wolf Trap last month, this is a recital not to be missed, especially since the program is an exquisite selection of late 19th- and 20th-century art song. The list of composers includes Barber, Poulenc, Mahler, Debussy, Musto, and Rachmaninoff, and not a chestnut among them. Tickets: $30.

>> The local new music group Great Noise Ensemble, whom we reviewed last year, opens its season on Saturday (September 29, 8 p.m.), in a concert with Duo46 featuring music by Berio, Adams, and others at Catholic University School of Music's Ward Hall.

THE FREE KIND:
>> On the airwaves this week, Front Row Washington (WETA 90.9 FM) on Monday night (September 24, 9 p.m.) will be a broadcast of pianist Till Fellner's excellent recital at the National Gallery of Art last winter. Also, WETA's Saturday opera broadcast (September 29, 1:30 p.m.) will be Washington National Opera's production of Duke Bluebeard's Castle and Gianni Schicchi from last fall.

>> On Tuesday (September 25, 12:10 p.m.), Ensemble Gaudior will perform on the free concert series at Church of the Epiphany (1317 G St. NW).

>> The Guarneri String Quartet continues its tradition of free rehearsals open to the public at Clarice Smith Performing Arts Center on Wednesday (September 26, 5 p.m.).

>> On Wednesday evening (September 26, 7:30 p.m.), violinist Alexander Gheorghiu and pianist Florian Müller will play a recital of music by Schoenberg, Webern, and Cage at the Embassy of Austria. Admission is free, but you must make a reservation.

>> On Thursday (September 27, 12:15 p.m.), pianist Grace Cho and a string trio will give a free cocnert at National City Christian Church (5 Thomas Cir. NW).

>> That evening (September 27, 8 p.m.), the University of Maryland Symphonic Wind Ensemble will give a free concert at Clarice Smith Performing Arts Center.

>> The Piano Society of Greater Washington will host its first concert and reception of the season on Sunday (September 30, 3 p.m.) at Calvary Lutheran Church in Silver Spring. These free concerts are offered "for the life-affirming love of music": a good-will offering is welcome, for upkeep of the piano.

WORTH MENTION:
>> The Washington Bach Consort will perform Bach's B Minor Mass, again, on Wednesday (September 26, 7 p.m.) at Strathmore.

>> Also Wednesday night (September 26, 7:30 p.m.), violinist Mariusz Patyra will play a recital at La Maison Française (4101 Reservoir Rd. NW).

>> Patyra will join with violinist Nicolas Kendall in an all-Bach program with the National Philharmonic Chamber Orchestra on Saturday (September 29, 8 p.m.) in the Music Center at Strathmore.

>> Pianist Carlos Rodriguez will be featured on the opening concert by the Alexandria Symphony Orchestra on Saturday night (September 29, 8 p.m.) at the Rachel M. Schlesinger Center in Alexandria.

>> The same evening (September 29, 8 p.m.), the a cappella vocal group The Countertop Quartet will give a benefit concert on behalf of the vendors of Eastern Market, at Saint Peter's Catholic Church (2nd and C Sts. SE).

>> For more concert information, go to Ionarts.