At the last Friday night Shabbat service I attended, the woman behind me was wearing a Grateful Dead T-shirt emblazoned with a skeleton face that had a joint dangling from its mouth. Two seats to my right, a man was talking about how he used to hang out backstage with the Dead because his buddy was the band’s pot grower. In the row in front me, two women dressed in hippie clothes were strumming guitars.

Was I in the right place?

“I thought I smelled patchouli,” my wife said.

We’re pretty sure she was mistaken, but it was easy for a person’s senses to get tricked at Congregation Etz Chayim’s Grateful Dead Kabbalat Shabbat service on the night before Halloween.

At times, I wondered if I was really in a cozy sanctuary in Palo Alto — or in a cloudy haze during an amazing second-set “Estimated Prophet” at Kaiser Auditorium in Oakland, circa 1985.

No, there wasn’t any pot-smoking going on at Etz Chayim — at least none that I saw or smelled — but many in the estimated gathering of 210 were clad in tie-dyed shirts and skirts, suede fringe vests, ’60s-style headbands and groovy shawls. I think I was the only one wearing a necktie, but I didn’t feel out of place: It was a trippy Grateful Dead tie.

There was a “dancing bears” blanket hanging above the bimah, a guy behind me yelled “Let Phil sing” and there were even a few people twirling at the back of the room — although if you’re not familiar with the Dead, those things probably mean nothing to you.

Me? I went to about 20 Dead shows from 1984 through 1995, the year of leader Jerry Garcia’s death. I wasn’t quite a Deadhead, but I definitely was excited when I heard about the (world’s first?) Grateful Dead Shabbat.

The event was part of Etz Chayim’s five-year-old Fifth Friday program: Whenever a month has five Fridays, Etz Chayim plans a musical or unconventional Shabbat service for the fifth one. Previous events highlighted the Beatles, Leonard Cohen, show tunes and Simon and Garfunkel, to name just a few.

And while a regular Shabbat service draws about 50 people, a good Fifth Friday gig pulls in three or four times that. For the Beatles event, an overflow crowd of 350 showed up, spilling over into the foyer and library. Not surprisingly, Beatles II is being planned for 2010.

On the night I attended, Grateful Dead songs pretty much formed the entire service, and they were incorporated in several ways. Most commonly, the congregation just sang them, backed by nine musicians and six chorus singers.

In those instances, we sang the songs as written, with a tweak or two here and there. For example, “What a long, strange trip it’s been” was changed to “What a long, strange week it’s been.” Each person had the lyrics in a meticulously prepared 30-page siddur.

Other tweaks included: “Yah’s got everything delightful. Yah’s got everything I need,” with Yah (God) replacing “she” in “Sugar Magnolia”; and “God bless!” instead of the commandment-breaking phrase in “Uncle John’s Band.”

Additionally, some songs were divided up into responsive readings, and some were used as silent meditations.

Each song was expertly picked for its spiritual meanings and adeptly placed within the liturgy by congregant-guitarist Mitch Slomiak. He also worked with rabbi-guitarist Ari Cartun on what was perhaps the event’s most creative aspect: adapting Hebrew prayers and songs to Grateful Dead tunes.

For example, “V’Shamru” was sung to the tune of “Truckin’ ” and L’cha Dodi to the tune of “Ripple.” It wasn’t always easy getting words and melodies to click, Slomiak and Cartun told me, but it was inspired nevertheless.

Afterward, at the oneg, a cake decorated with the Dead’s iconic, colorful dancing bears was a big hit, and lines of people from as far away as El Cerrito congratulated Cartun and band members on such a fun and special night.

My only dismay: No typical Grateful Dead scene in the parking lot beforehand. Oh, to have seen Deadheads peddling matzah balls instead of hallucinogenic goo-balls.