What's a jazz festival for, anyway? After last month's Monterey Jazz Festival, a dazzlingly successful event with at least half a dozen musical epiphanies squeezed into just one weekend, the question seems unavoidable when looking over the schedule for the San Francisco Jazz Festival, which opens its 26th season this weekend.

Rather than gathering hundreds of musicians in one location for a brief, glorious burst of music, the San Francisco event is essentially a concert series that offers a handful of performances every week or so through Nov. 9. Since the mid-'90s, this event has often been ranked as the most respected jazz festival in the United States. But this season some of the mojo seems to be wearing off, with a lineup that lacks a critical mass of eagerly anticipated performances.

Granted, even in an off year, the festival provides a wealth of music. It opens Friday with a reprise of last May's thrilling, sold-out "Miles From India" concert. What's missing this season is the sense of urgency that comes from capturing some facet of what's happening in jazz right now. The majority of the jazz artists could (and have) fit nicely into the programming at Yoshi's San Francisco and its older Oakland sibling, so what's the added value of seeing the artists in the context of the festival?

SFJazz, which presents the festival, continues to pursue the purchase of a building that will allow it to present artists completely on its own terms, and which may enable the organization to book musicians who aren't otherwise financially viable for the festival. Now SFJazz uses nearly a dozen theaters and clubs around town. The profusion of venues may diffuse the festival's energy, but it also offers opportunities for matching artists to an appropriate site.

German retro crooner Max Raabe and the Palast Orchester, for instance, perform at Oakland's Paramount Theatre Oct. 18, bringing Weimar-era opulence and irony to the stunning art-deco setting. And the powerhouse Cuban vocalist and bandleader Issac Delgado performs two show with his hard-hitting timba band at Bimbo's, the ornate 1930s-style supper club with a spacious dance floor.

"We're lucky we use a bunch of different halls," says Randall Kline, founding artistic and executive director of SFJazz. "Each one has specific restrictions and characteristics. Grace Cathedral has that six-second echo, and we've taken advantage of the acoustics and built an audience around presenting artists there. Our Yerba Buena Center for the Arts Forum shows are geared toward a younger audience. It's a clubish feel and a less formal vibe, so that's where we're presenting Ravi Coltrane."

As an organization, SFJazz has done many things right. The education program has helped raise a generation of savvy jazz fans and players, topped by the SFJazz High School All-Stars, the region's premier proving ground for elite teenage jazz talent. The SFJazz Collective, which performs as part of the organization's Spring Season, is sounding better than ever, despite the exit of founders Joshua Redman, Bobby Hutcherson and Nicholas Payton in recent years.

One relatively disappointing lineup doesn't undermine the viability of the SFJazz festival model, particularly with its strong track record, but it certainly raises questions. It's telling that the artists featured this year tend toward chronological extremes, with the vast majority in their 30s and 40s or 70s and 80s. Only three of headliners jazz artists fall between 50 and 65, the period when jazz musicians are often doing their best work and are most likely to be overlooked. These are exactly the artists who are unlikely to work in San Francisco without an SFJazz forum.

In past years, the festival has occasionally showcased a particular artist in several contexts. Other times, through planning or happenstance, the festival presents an array of musicians on a particular instrument, offering an incisive look at the past, present and future of, say, jazz piano or tenor saxophone.

I won't harp on the festival's perennial dearth of Bay Area artists. Kline argues persuasively that the event is best at reflecting the local scene, rather than building it. But with a little imagination, and partnering with grass-roots organizations like Intersection for the Arts or Red Poppy Art House, the festival could help raise the visibility of local masters such as saxophonist George Brooks, clarinetist Ben Goldberg, saxophonist Harold Wiley, vocalist Kenny Washington, trumpeter Sarah Wilson, bassist Lisa Mezzacappa and saxophonist Phillip Greenlief. If a festival is doing its job, it leaves the scene better off after the last chord has sounded.

By Andrew Gilbert