NEW YORK – Phish, the Burlington, Vt.-based jam band whose legions of dedicated fans made them one of the nation’s top touring acts, announced Tuesday that they were breaking up.

The surprise announcement came as the band prepared to release a new album, “Undermind,” on June 15 and embark on a summer tour, which will kick off June 17 at Coney Island in Brooklyn, a borough of New York City.

Band leader Trey Anastasio made the announcement on the band’s Web site.

“Last Friday night, I got together with Mike, Page and Fish to talk openly about the strong feelings I’ve been having that Phish has run its course and that we should end it now while it’s still on a high note,” he wrote.

The quartet, which includes Anastasio, Jon Fishman, Mike Gordon and Page McConnell, was formed in 1983. The band drew thousands of fans to its concerts with marathon performances and long, experimental jams that melded a wide span of genres, from bluegrass to electronica.

Some shows drew up to 80,000 fans and, for many of them the band became the center of their universe. Much like the fans of the Grateful Dead before them, fans would follow the band from show to show. Phish’s encouragement of the taping of their concerts also endeared them to their audiences.

Phish went on a two-year hiatus in 2000. In the interim, band members delved into various solo projects. Anastasio has released three solo albums, including his latest, 2004’s “Seis De Mayo,” while Gordon released his solo debut, “Inside In,” last year.

Phish ended their hiatus with a series of shows at New York City’s Madison Square Garden. The first was on New Year’s Eve 2002.

Anastasio called that hiatus an attempt to revitalize themselves. But he said that was no longer an option.

“We don’t want to become caricatures of ourselves, or worse yet, a nostalgia act,” he said. “By the end of the meeting, we realized that after almost 21 years together we were faced with the opportunity to graciously step away in unison, as a group, united in our friendship and our feelings of gratitude.”

Phish will end their tour in Coventry, Vt., in a two-day festival Aug. 14-15 at Newport State Airport. That concert, announced earlier this month, was initially expected to attract 70,000 fans, but could draw many more in the wake of the breakup announcement.

“We are proud and thrilled that it will be in our home state of Vermont,” Anastasio said. “It’s been an amazing and incredible journey. We thank you all for the love and support that you’ve shown us.”