"Mozart and His Time," a citywide festival celebrating the bicentennial of his death, will take place in San Francisco May 22-June 30, 1991. The festival represents a historic collaboration of 42 San Francisco arts organizations, the largest such assemblage in the city's history.

Leading off the celebration in six broad categories (vocal, instrumental, dance, theater, humanities and new and unusual Mozart) are the four largest participating organizations: the American Conservatory Theater, San Francisco Ballet, San Francisco Opera and San Francisco Symphony. SFO general director Lotfi Mansouri, who instigated the project, is chairman. Mayor and Mrs. Art Agnos are honorary chairpersons of the festival, and Ann Seamster is festival manager.- DONALD RUNNICLES has been appointed music director of the San Francisco Opera, effective in January 1992. He will serve as music director designate beginning January 1991, overseeing orchestra auditions and other artistic matters. Sir Charles Mackerras will be principal guest conductor beginning in 1993. Both appointments will run through 1995.

Runnicles, who is music director in Freiburg, Germany, made a big public and artistic hit in his SFO debut last June, leading two complete cycle of Wagner's Ring. His many credits since 1980 include Mannheim, Hamburg and the Metropolitan operas, and he is scheduled soon at Glyndebourne, Vienna State and the Met.

- SINGERS AND OTHER ARTISTS of the San Francisco Opera Center will tour the Japanese cities of Nagaoka, Sendai and Murioka next spring. Patrick Summers is music director.

- AT SANTA FE OPERA, Barbara Zarlengo has been appointed executive director, succeeding Philip Seamark, effective this coming January. She is currently director of development at New York City Opera.

- GIAN CARLO MENOTTI, 79, will continue for the present as artistic director of the Spoleto USA festival, after resolution of a dispute over the director's authority. A tentative agreement has been reached to ensure the composer's lifelong involvement with the festival he created in 1977, patterned after the Festival of Two Worlds in Spoleto, Italy.

- BOLSHOI BALLET director Yuri Grigorovich has formed a new company of young Russian dancers, ages 19-25, the first to be independent of state subsidy and control. The 60 dancers are projected to be entirely self-sufficient, deriving income from performance in Russia and on tours abroad, including the United States, where they were to make their debut in Texas this past week. As they mature artistically, they will be advanced into the Bol-shoi Ballet.

- WHAT THE NATIONAL GALLERY describes as the first exhibition in more than half a century to cover Titian's long and influential career, "Titian, Prince of Painters," is now on show there through Jan. 27, 1991.

The exhibition commemorates the 500th anniversary of the Venetian Renaissance master's birth - widely accepted as 1490.

It brings together nearly 50 of his paintings and three of his ceilings, one of them mounted with the 19 panels that originally surrounded it. The works have come from many European sources.

The exhibition was first shown in Venice earlier this year and will not be shown anywhere else.