Jerry Garcia, whose gentle voice and gleaming, chiming guitar lines embodied the psychedelic optimism of the Grateful Dead for three decades, died in his sleep yesterday at Serenity Knolls, a residential drug treatment center in Forest Knolls, Calif. He was 53.

A spokesman for the band, Dennis McNally, said the cause was a heart attack.

The guitarist had suffered serious health problems for a decade. In the 1960′s, he was known as Captain Trips, referring to his frequent use of LSD, and he struggled through the years with heroin addiction. He was hospitalized in 1986 in a diabetic coma, and in 1992 the group had to cancel tour dates when Mr. Garcia fell ill from exhaustion. In recent years he had tried to stop smoking and to lose weight.

The Grateful Dead, and Mr. Garcia as their most recognizable member, had come to represent the survival of 1960′s idealism. As news of his death spread, fans wept in the streets of San Francisco and the Internet was flooded with eulogies and reminiscences.

Within the music business, the Dead exemplified integrity in a sphere of hype and artifice; beyond, they symbolized a spirit of communal bliss, with free-wheeling, anything-can-happen music to bring together a community of tenacious fans, the Deadheads.

The band’s future is uncertain; the Dead had planned to record their newest songs in a studio for an album to be released next year.

The Grateful Dead were one of rock’s most beloved institutions. Formed in 1965, when a Bay Area jug band decided to switch to electric instruments, the Dead created an all-American fusion of bluegrass, blues, country, rhythm-and-blues, folk and rock, all laced with improvisation. The band never played a song the same way twice.

The Dead built their reputation on long, free-form concerts, going onstage without a set list and playing anything from original songs to rock oldies to extended experiments with feedback. The music could shift in any direction as it sought what the band and its fans called the “X factor”: spontaneous, revelatory stretches of music arrived at through practice and serendipity.

The Dead were one of the top bands in late-1960′s San Francisco, and unlike their hippie-era contemporaries, they continued to thrive, their essence unchanged and their popularity expanding. John Scher, chairman of Metropolitan Entertainment, which coordinates the band’s East Coast performances, said yesterday that the Grateful Dead “are unquestionably the highest-grossing band cumulatively in the history of the music business.”

He noted that the band in recent years played 85 to 110 shows annually. It set attendance records for every major arena in the New York area, as well as the Spectrum in Philadelphia and the Boston Garden.

The Dead’s fans savored the group’s unpredictability, seeing as many concerts as possible and sometimes following the band for a full-length tour. For most of the 1980′s and early 1990′s, the band toured stadiums and did not play to a single empty seat; some concerts sold out before they were advertised, purely through announcements in the Deadheads’ newsletter and on a telephone hotline. (The band had planned six concerts in late September at Madison Square Garden as part of a fall tour, but it is unclear if they will proceed.)

Unlike the vast majority of rock bands, the Dead focused on performing rather than recording. Even as a stadium attraction, the Grateful Dead were something like an old-time jug band, barnstorming a territory that stretched around the world.

Mr. Garcia was at the heart of the Dead’s music. His reedy voice was unassumingly sincere; his guitar tone was pristine and bell-like, as he spun long, leisurely lines with distinctive curlicues and downward slides. He wrote about half of the Dead’s own material, working primarily with the lyricist Robert Hunter, and many of his finest tunes — such as “Ripple,” “Touch of Grey,” “China Cat Sunflower” and “Uncle John’s Band” — sounded as natural as traditional songs. Mr. Garcia’s smiling, bearded face became an icon of a utopian 1960′s spirit.

Jerome John Garcia was born in San Francico on Aug. 1, 1942. His father was a professional musician, and he took piano lessons as a child. But he lost most of the third finger on his right hand in a childhood accident. When he was 15, he heard Chuck Berry and took up the electric guitar. After nine months in the Army, he turned to folk music, picking up the banjo and playing in bluegrass bands; he also studied at the San Francisco Art Institute. By 1964, he was in Mother McCree’s Uptown Jug Champions, which also included Bob Weir on guitar and Ron (Pigpen) McKernan on harmonica.

A year later, with Phil Lesh on bass and Bill Kreutzmann on drums, the band plugged in and became the Warlocks. At first, they worked as a bar band, playing blues six nights a week. The Warlocks soon changed their name to the Grateful Dead — a type of British folk ballad in which a human being helps a ghost find peace — after running across the phrase in a dictionary. They became the house band for Ken Kesey’s Acid Tests, the public LSD parties held before the drug was outlawed.

The Dead lived communally in San Francisco and played many free concerts, soon working their way up to the city’s ballrooms and the Fillmore West. The band signed a contract with MGM Records in 1966, but its efforts were shelved. In 1967, the Dead signed with Warner Brothers, and while their first albums sold modestly, their reputation spread. From the beginning, when the band was financed by the LSD chemist Stanley Owsley, the Dead were known for the latest in sound systems as well as for their music. The group performed at the Monterey Pop Festival in 1967 and at Woodstock in 1969.

By 1970, the Grateful Dead had made five extraordinary albums in a row: “Anthem of the Sun” in 1968, “Aoxomoxoa” in 1969 and “Live Dead,” “Workingman’s Dead” and “American Beauty” in 1970. Its 1971 live album, “Grateful Dead,” became its first million-seller, and it continued to play to larger and larger audiences. In 1973, it was one of the three groups (with the Allman Brothers Band and the Band) to perform for half a million people at Watkins Glen, N.Y.

Mr. Garcia also worked outside the Grateful Dead, as a musician and a producer. He recorded with the Jefferson Airplane and Crosby, Stills, Nash and Young; he produced the first album by the New Riders of the Purple Sage, adding parts on an instrument he was just learning, the pedal steel guitar.

Outside the Dead, Mr. Garcia pursued some of the styles that were tucked into the Dead’s music. In the early 1970′s, he played jazz-rock with the keyboardist Merl Saunders and bluegrass with a group called Old and in the Way; he also recorded his first album as a leader in 1971, playing rock songs tinged with country. Through the years, he toured (between Grateful Dead tours) with his own band, and he collaborated with musicians including the keyboardist Howard Wales and the mandolinist David Grisman.

His most recent recording, released in 1993, was an album of children’s music, “Not for Kids Only.” In another recent project, Mr. Garcia designed a line of neckties that was sold at Macy’s and other stores.

Yet most of his time was devoted to the Grateful Dead. While the band had touched on funk and jazz, and had incorporated some of the new sounds made available through synthesizer technology, its music remained immediately recognizable, with a folksy, homespun tone that belied the size of its audiences. Grateful Dead concerts are among least overbearing in current rock; the band’s customized sound systems emphasize clarity and warmth, not sheer volume. Through the years, the Dead’s tour circuit expanded, including a 1978 series of shows at the Great Pyramid in Egypt; the band toured with Bob Dylan in 1987, a collaboration that resulted in a live album. The band weathered the deaths of Mr. McKernan in 1973 as well as the deaths of two of its keyboardists, Keith Godchaux and Brent Mydland.

Since the 1970′s, the band has attracted a significant following of Deadheads, which expanded further in the 1980′s as the sons and daughters of baby boomers embraced the band as a symbol of 1960′s pleasures and hopes. The Dead made an effort to treat their fans well. Unlike many bands, the Dead encouraged their fans to tape their concerts, even providing a place near the sound engineer’s booth for fans to set up microphones and tape recorders. They also kept ticket prices low and maintained contact with fans through the newsletter, a hotline and, more recently, electronic mail. In return the Dead have held on to what is probably the longest-lasting mass following in rock history.

In tie-dyed clothes and bare feet, dancing in the aisles, the Dead’s audiences revived the wardrobe, and perhaps some of the hopefulness, of the Summer of Love. In an interview for Joe Smith’s book “Off the Record” (1988), Mr. Garcia said, “To the kids today, the Grateful Dead represents America: the spirit of being able to go out and have an adventure.”

He is survived by his third wife, Deborah Koons Garcia, and by four daughters: Heather, Annabelle, Teresa and Keelin, all of Marin County.