(RNS) — A half-century ago, when civic groups were a staple of American life, 4.1 million men regularly spent evenings at Masonic lodges around the country. That period, from the late 1950s to the early 1960s, would be the peak of Freemasonry membership.

Each year since, membership has declined, in line with those of other service organizations. The current membership? 1.4 million.

Now, though, Masonic leaders are hoping that the publication of novelist Dan Brown’s latest thriller, “The Last Symbol,” whose plot is tied to Masons, will revive interest in the group.

Masonic lodges are hosting open houses to help accommodate curious visitors, and in Washington, D.C., the landmark Scottish Rite temple near the White House is bracing for busloads of tourists.

On Saturday (Oct. 3), Washington-area Masons held an unusual “Masonic Day of National Prayer” with a decidedly Christian feel at a prominent United Methodist church.

“This is where Dan Brown got it so wrong. … Masons are not looking for a symbol, which by definition must point to something else,” said Most Worshipful Brother Rev. Terry Tilton, a retired Masonic leader from Minnesota, during the service.

“There can be no real substitute for perfection, the infinite and divine truth. And that is why just because God is God and we are not, human beings can never fully bridge the gulf of understanding and perfection in this world.”

Word that Brown would feature Masons in his newest novel did not initially please some Masons. After all, the author is still viewed as villainous in many Catholic circles for sinister portrayals in “The Da Vinci Code” in 2003 of the lay Catholic group Opus Dei, another group that, like Masons, has long been viewed as overly secretive.

“The world seems to have today a schizophrenic mind about Freemasonry,” Tilton said. “There seems to be an alternating fascination and loathing of our fraternity.”

After reading reviews of “The Lost Symbol,” however, Masons seem more likely to hold a “Dan Brown Appreciation Day” than to bad-mouth him. Treatment of Masons in the new novel, released last month, is generally positive.

“From what I’ve read, it’s not that critical of Masons, it’s just a couple of rogue Masons going against the code of what we believe in,” said Mike Rems, secretary of the Jersey City (N.J.) Masonic Lodge. “Dan Brown actually respects the Masons.”

Historians disagree on the Masons’ origins. Many believe the first ones were in organized groups of medieval stonemasons. After 1717, when the first Grand Lodge of England was founded, the group became easier to trace. Through the three ensuing centuries, it has been an international fraternal and service organization requiring members to believe in a supreme being, irrespective of which religion, if any, they claim.

“The Lost Symbol” involves the leading figure in Brown’s previous books, Harvard symbologist Robert Langdon, trying to save his mentor, a prominent Mason, in a code-ridden adventure set in Washington, D.C.

Members know the conspiracy theories that abound: that Masons have plotted to overthrow governments, favor a New World Order, promote Jewish interests, worship Satan, have placed secret codes in public places, and inform only high-level members about these matters.

Like Opus Dei, the Masons have been subject to conspiracy theories long before Brown used them as plot fodder. And both groups saw the need to react to publicity from the respective books.

“Dan Brown’s treatment of Freemasonry is overwhelmingly positive in `The Lost Symbol,’ but he does engage in some dramatic license for the sake of his plot,” group leaders wrote on a new Web site, freemasonlostsymbol.com, set up by the Masonic Society, the Masonic Service Association of North America and the George Washington Masonic Memorial.

If nothing else, members of the graying, aging movement say the Brown novel has provided a psychological shot in the arm, and the opportunity to go public with their beliefs without all the baggage Catholics faced with “The Da Vinci Code.”

“At least Dan Brown got it right when … Langdon told (a character in the book) ‘For the record, madam, the entire Masonic philosophy is built upon honesty and integrity,”‘ Tilton recalled from the new novel. “Masons are the most trustworthy men you could ever hope to meet.”‘

(Jeff Diamant writes for The Star-Ledger in Newark, N.J.)