SAN FRANCISCO (Reuters) - Saying Barack Obama embodies political hope absent since Robert Kennedy was slain 40 years ago, three surviving members of the Grateful Dead rock band reunited on Monday for the first time in four years to back the presidential candidate.

“Every few generations a guy like this comes along,” drummer Mickey Hart told a news conference a day before California’s primary, in which Obama, a senator from Illinois, faces New York Sen. Hillary Clinton. “It seems like desperate times and we’re desperate people.”

The counter-culture band, known for its loyal “Deadhead” fans, broke up in 1995 after the death of its leader, guitarist Jerry Garcia. They have since played together occasionally, most recently in 2004.

At a San Francisco concert in front of 2,400 fans, singer-guitarist Bob Weir, 60, said the band had never before, performed on behalf of a presidential candidate, although they have often embraced liberal social causes.

“The last time hope was in the air, it was ended by a bullet,” Weir said, referring to Kennedy, who was assassinated on the night he won the California Democratic primary in 1968. “We’ve been reluctant to do political events all along.”

Bassist Phil Lesh, 67, said he met Obama, who told him he has some Grateful Dead songs on his iPod music player, last year.

The concert started with a short video from Obama, filmed on an airplane, thanking the band. A thick cloud of marijuana smoke wafted through the air then and throughout the concert, and some fans engaged in free-style dance as though magically transported from 1968.

Obama’s dapper, clean-cut image contrasted with the tied-dyed shirts and long, shaggy hair of fans who lined up for hours to attend the “Deadheads for Obama ‘08” event.

“Long live the Dead!” said Ron Svetlik, 51, who said he had attended more than 200 Grateful Dead concerts, starting in 1974.

The home builder said he had already voted by mail for the Green Party candidate, but added: “If I had to cast a write-in ballot, I’d put Jerry Garcia.”

The three band members neither promised more concerts nor ruled them out. “It’s a lot like family,” Weir said, referring to complicated relationships dating back more than 40 years. “What we have is thicker than blood.”