BOSTON, AUG. 1 -- The "art wars" opened a front in Boston today with the showing of the controversial retrospective of photographs by the late Robert Mapplethorpe and quickly settled into an uneasy truce.

Indeed, the city's artistic and gay communities -- working behind the scenes and in public -- have joined forces to head off any threats to the exhibit, which opened this morning at the Institute for Contemporary Art in Boston's Back Bay section.

After weeks of buildup that included threats by some conservative groups, dueling press conferences and extensive news coverage, the opening was something of an anticlimax. A lone protester was surrounded and drowned out by hundreds of supporters asserting free speech and denouncing censorship.

The furor over the Mapplethorpe show began in Washington in June 1989 when the Corcoran Gallery canceled its showing of the exhibition. When the retrospective traveled to Hartford, Conn., and Berkeley, Calif., it met with little objection. But in Cincinnati, the Contemporary Arts Center and its director, Dennis Barrie, were indicted on obscenity charges and face trial this fall.

Here, where the phrase "banned in Boston" is not such a distant memory, there was great suspense about how the show would be received.

"I feel great," ICA Director David Ross said shortly after the opening, noting that ticket sales were brisk and that membership had surged by 50 percent in the last month.

Outside in the ticket line, Alexander Schiller, a Russian emigre from nearby Brookline, said he was there simply because "I wanted to see for myself."

Across the street, supporters walked a picket line and displayed a giant puppet in the shape of the Statue of Liberty. Peter Desmond, a songwriter from Cambridge, said he was there to support freedom of expression.

Two young men from the militant gay rights group ACT-UP said they were battling censorship and homophobia.

"We're here to make the point that art is not obscene -- that nothing about the human body is," said Ed Boyce of Boston. "Those who would like to shut the exhibit down are homophobes and bigots. If they can stop a piece of art, there's no limit to what can be suppressed."

According to Ross, the sidewalk demonstration of support was just one ingredient in the successful opening. "I've felt very good about the way this city has been responding for some time now," the museum director said.

He pointed to the support the ICA has received from the city's other museums, the corporate sponsorship it has enjoyed for the Mapplethorpe show and the decision by law enforcement authorities not to prosecute.

Attorney General James Shannon, a liberal Democrat running for reelection, spoke out early and forcefully, saying he would take no action against the Mapplethorpe show.

"In my view, this exhibit shouldn't be prosecuted because it doesn't fall within the definition of what's obscene under state law," Shannon said last month. "The laws were written so as not to have public officials tell museums what is art and what isn't art."

The administration of Boston Mayor Raymond L. Flynn has quietly cooperated with the museum, working with Ross on crowd control and security concerns. Suffolk County District Attorney Newman Flanagan refused to say in advance what he would do, but he took no action today.

And while the official publication of the Boston Roman Catholic archdiocese editorialized against the show, Cardinal Bernard Law has not spoken on the controversy.

At the same time, several groups that have expressed outrage over the show and threatened action have apparently decided to hold their fire for now.

At a statehouse press conference Tuesday, representatives of Morality in Media, Citizens for Family First, the Catholic League for Religious and Civil Rights and others limited themselves to calling on law enforcement officials to take action.

At the core of the controversy are seven photographs out of the more than 120 in the exhibit. Five of those seven depict deliberately shocking homosexual sex acts, and the other two show a nude and a semi-nude child. The bulk of the exhibit consists of formal studies of flowers, portraits and adult nudes, often infused with an erotic air.

The show's opponents told reporters they were outraged by those seven photos and disavowed any interest in censoring Mapplethorpe.

"I'm not here because I hate homosexuals. I don't," the Rev. Earl Jackson Sr., a Boston minister who heads the Exodus Movement activist organization, said at the opponents' press conference. "We object to our tax dollars being used to promote art such as that in the Mapplethorpe exhibit."

Philip Lawlor, director of a conservative lay Catholic group, said that if prosecutors did not act, "an aroused citizenry will take whatever steps are required to remedy that deficiency." He would not elaborate.

In Boston, where it is still illegal to sell liquor on Sundays, the original settlers were English Puritans who did not hesitate to ban dancing, Sabbath-breaking and other dangerous diversions. Their role as a conservative influence has been inherited by elements within the Catholic Church and, more recently, by some small groups on the religious and political right.

But Boston also has a long tradition of reformism and liberal -- if not radical -- political thought, and it serves as home for a large gay community and a vibrant artistic community with ties to the area's many universities.

Thus, the ICA found itself with plenty of allies. The city's arts establishment has closed ranks, and the museum discreetly paved the way for the show. The museum hired Larry Rasky, a Democratic political consultant, who said he handled "political trouble-shooting" before the opening.

Not by accident, the Mapplethorpe opening coincides with a special exhibit at Boston's influential Museum of Fine Arts devoted to depicting

the human form and a separate Mapplethorpe show at Harvard's Fogg Art Museum. In addition, the Photographic Resource Center has mounted two shows intended to amplify the debate over art, sex and censorship.

The showing of "Robert Mapplethorpe: The Perfect Moment" in Boston is the eighth and final stop of the exhibit, which was organized by the ICA of Philadelphia in 1987.

Mapplethorpe died of AIDS on March 9, 1989, at Deaconess Hospital in Boston. At the time of his death, he was an obscure figure to most Bostonians. Today, thanks to the new-found notoriety of his work, he is a celebrity.