The New Covenant Church in this heavily Roman Catholic and blue-collar city entered a float in the annual fall chrysanthemum parade like no other float in the lineup: a yellow school bus draped with a 30-foot-long poster of a fetus.

Clowns walked beside the float handing out white balloons printed with the message, "Vote Yes for Life."

Today's referendum here on Roe v. Wade -- apparently the first referendum on the Supreme Court's 1973 decision upholding a woman's right to abortion -- is nonbinding, but laden with symbolic significance. One side hopes, and the other fears, that Bristol's vote could trigger similar votes in other communities whose weight would force a constitutional amendment.

"Just think of what happens if we win. This will be another nail in the coffin of Roe v. Wade," said Rev. Patrick Mahoney, 31, pastor of the fundamentalist New Covenant Church and spokesman for Celebrate Life, the local antiabortion group pushing the referendum. "What if this continues? Suppose you have a national referendum in 1988?"

At least two other communities have picked up the beat. Since Bristol's City Council agreed last August to put the question on the ballot, similar measures have been put on the ballots in Dover and Derry, N.H. In Bristol, it reads, "Should the decision of the Supreme Court regarding abortion be overturned?"

"This is only the beginning," said Catherine Blinder, 35, campaign manager for Citizens Against Referendum One (CARE1), a community "pro-choice" group. "If we lose the battle here in Bristol and we continue to lose battles on other referenda, we'll be forced into a retrenchment. We'll be forced to protect what we've already won."

Such portent seems out of place in Bristol's small-town atmosphere. Riding an economic boom in its bicentennial year, this city of about 58,000 was chosen recently as home for the cable Entertainment and Sports Network (ESPN) and is becoming a commuting hub for nearby Hartford. But almost everyone still seems to know almost everyone else.

Politically, Democrats outnumber Republicans 3 to 1.

"In their personal lives, Bristol people are very conservative, but they tend to vote like liberals," said former Republican mayor Michael L. Warner, 35, director of the Chamber of Commerce.

An estimated 60 percent of Bristol's residents are Roman Catholic, and the city's five Catholic priests have urged support for the referendum.

"They couldn't have picked a better town to do this in," Blinder said of Mahoney and his group.

Mahoney, who moved to Bristol 3 1/2 years ago from Florida, denies that he handpicked his new home town with an eye to a referendum.

"They give us too much credit," he said. "We're just local people."

The referendum is the result of a compromise after Celebrate Life sued the City Council for refusing to place on the ballot six proposed ordinances imposing local regulations on abortions, including anesthesia and burial for the fetus, and the filing of abortion records at City Hall. The suit was dropped, and pro-choice advocates helped draft the referendum.

Both sides have waged aggressive campaigns. A poll published yesterday in the Bristol Press showed 36.6 percent for the referendum and 39.6 percent opposed; 5.8 percent refused to answer and 17.9 percent were undecided.

Few shoppers questioned on a recent day at the city's Centre Mall found the referendum, even though toothless, unimportant.

"It won't be able to do much good either way," Lucille Rajotte, 65, said. "But I think it's good that it's on the ballot. It makes people stop and think about it."

Democratic Mayor John D. Leone said he has kept the issue out of his reelection campaign.

But "if it . . . lets people voice their opinion, then I feel good about it," Leone said. "It's an intense issue, one that strikes at the heart and soul of a lot of people. It's not going to go away."