WASHINGTON – Call Joe Lieberman the unlikely evangelical.

The Independent senator from Connecticut – and the best-known Orthodox Jew in American politics – is probably more cognizant than most of his Jewish congressional colleagues about rabbinical interdictions against encouraging non-Jews to mimic Jewish ritual.

Yet here he is, about to release a book advising Christians and others not to drive to church, to welcome their Sabbath in the evening, to cut off the wired world and to, umm, enjoy your significant other.

Upon meeting with Lieberman in his Senate offices last week, before the Aug. 16 release date of his new book, “The Gift of Rest: Rediscovering the Beauty of the Sabbath,” he laughed at the term “evangelical.” It’s not that he wanted to convert anyone, Lieberman emphasized.

“This gift, I wanted not only to share with Jews who are not experiencing it, who haven’t accepted it, but also in some measure to appeal to Christians to come back to their observance of their Sabbath on Sundays,” he said.

Lieberman does so in an engaging read, melding an unlikely array of tales – ranging from 16th-century Safed to tension-soaked Republican and Democratic back rooms – making the case for a structured day of rest that offers freedom within iron walls.

The book also provides a glimpse into how religion shaped this most adamant of congressional centrists, whose stubborn hewing to his beliefs brought him within shouting distance of the vice presidency before propelling him toward the end of his political career (Lieberman announced in January that he will not seek re-election in 2012).

One example of Lieberman’s championing of freedom through restrictions is how the dictates of the holy day liberate him from his BlackBerry.

“If there were no Sabbath law to keep me from sending and receiving email all day as I normally do, do you think I would be able to resist the temptation on the Sabbath? Not a chance. Laws have this way of setting us free,” Lieberman said.

As it turns out, this has been a book Lieberman has been considering for a while. He says the seeds of it reach as far back as his first run for state senator in 1970, when his Sabbath observance first created logistical problems for his campaign staff. It emerged full force when Al Gore named him as his running mate in 2000.

Conversations with Christians and their curiosity about his observance crystallized the idea for the book, he told JTA.

“This is something I thought about doing for a long time,” Lieberman said, “because the Sabbath has meant so much for me. It’s really been a foundation for my life.”

The book is published by Simon & Schuster’s Howard imprint in conjunction with Orthodox Union (O.U.) Press. Lieberman co-wrote it with David Klinghoffer, a conservative (and Orthodox Jewish) columnist and author, and consulting with Rabbi Menachem Genack, who runs the Orthodox Union’s kashrut division and with whom Lieberman takes a weekly telephone class.

Genack in an interview downplayed the book’s outreach to Christians. “He really wants Jews to read it; he wants to bring the beauty of Shabbos to his own constituency,” said Genack. “But that message and that beauty has a universal theme as well.”

Each chapter ends with a list of “simple beginnings” – practices that could launch a reader’s observance: “Turn off the TV, computer, cell phone or all three”; light two candles; bless your children, “placing your hands on their head or shoulders”; and “consider choosing a congregation close enough that you can walk there and home again.” In one chapter he describes God’s “brilliance” in mandating conjugal sex during the Sabbath.

Lieberman’s growth as an observant Jew and his frustrations and triumphs as a politician weave through the book. He withdrew from observance at Yale University, but the death of his beloved maternal grandmother in 1967 returned him to the Sabbath observance of his upbringing. Within three years, at age 28 and with his Yale Law buddy Bill Clinton assisting him on the campaign, he won his first elected office, Connecticut state senator.

“I began to see myself in the larger context of history,” Lieberman said. “I came back step by step to observance.”

His Jewish observance inevitably seeped into his public life, and he writes vividly of how it influenced his decision in 1998 to chastise Clinton from the Senate floor for his affair with intern Monica Lewinsky. He recalls discussing with his family whether to be the first major Democrat to speak out. His four children said he should; Hadassah, his wife, was torn; his mother, who adored Clinton, urged him to keep silent.

In the end, his rebuke that the president’s behavior was “immoral” and “harmful” and “too consequential for us to walk away from” made history. This break with the Democratic consensus helped lead Gore to choose him as a running mate in 2000; Lieberman represented a clean break with the scandals that had dogged Clinton.

Many of these episodes seem bittersweet. He writes of the celebratory Sabbath he shared with Al and Tipper Gore on Dec. 7, 2000, when the Florida Supreme Court ruled in favor of a recount that almost certainly would have propelled Gore to the presidency and Lieberman to the vice presidency. The Liebermans rushed to the Naval Observatory, the vice president’s residence, just in time for Shabbat candle lighting, and after dinner the two couples walked the mile or so back to the Lieberman home in Georgetown.

“It was a night when we felt at the door of history and also very close to these two fine people,” he writes, and stops there. It’s as if he can’t bring himself to the denouement: The door that history opened was not to occupancy of the Naval Observatory but to a profoundly divisive U.S. Supreme Court decision overruling the Florida court that would put George W. Bush in the White House.

It’s a fluke of the fates keenly felt by his friends; Genack corrects me when I call Lieberman “the first Jew on a major ticket.” “He was the first Jew elected vice president,” he says. “He was elected vice president.”

The book’s political content is hardly a settling of scores. If anything, it is what Israelis call a “heshbon nefesh,” an accounting of a soul.

Lieberman ends the Lewinsky episode by emphasizing that he did not vote for impeachment and regarded the former president as “capable of genuine goodness, even greatness.” He is effusive in his praise of Gore, although the former vice president shocked Lieberman by endorsing Howard Dean, Lieberman’s nemesis, in the 2004 election.

The book’s fond recollections of Democrats throughout obscure his painful break with the party in 2006, when he lost his state’s primary election and ran for senator as an Independent. Oddly, that episode is not mentioned.

Occasionally a regret seeps through: Describing the village-like atmosphere of his Washington synagogue, Lieberman notes in the book that he and a journalist he once regarded as a friend now barely exchange hellos, and that another friend still chides him for voting to go to war with Iraq in 2002 – a war that most American Jews eventually came to oppose.

That’s not the only hint of the Joe Lieberman that has driven crazy many liberal American Jews who otherwise felt great pride in his rise. Lieberman praises John Hagee, the evangelical pastor who founded Christians United for Israel and whose excoriations of President Obama and other Democrats have turned off much of the Jewish establishment.

And there’s material to drive Jewish conservatives crazy. Explaining his Sabbath compromises, he says that voting for social welfare programs on Shabbat amounted to “pikuach nefesh,” saving of lives, which mandates violating Sabbath prohibitions.

Lieberman says he does not regret striking his own path down the middle.

“It’s certainly made me more productive as a senator,” he says.

Perhaps, but it was his closeness to Bush and his Iraq War advocacy that drove him out of contention for the presidential nomination in 2004. The legacy he now longs for, exemplified by this book, has supplanted the legacy that his independence cost him: first Jewish president.

“I feel that this book may be one of the most important things I do in my lifetime,” Lieberman said. “It’s from really inside me. I hope it affects people’s lives.”