The debate may have divided residents of Chappaquiddick, but the Martha's Vineyard Commission voted unanimously last night to designate the little island at the eastern end of Edgartown as a district of critical planning concern (DCPC).

Given Chappaquiddick's winter population of about 125 residents, the turnout was notable. Well over 100 people filled the ground floor of the Whaling Church, and then waited almost 9:30 p.m. for the Chappaquiddick issue to come to the fore.

It wasn't until 11:30 p.m., after hours of back-and-forth discussion, that the weary commissioners voted in favor of the DCPC, setting into motion a process which proponents hope will protect the island's rural character.

"Our unique values are being threatened," said Don Crocker, president of the Chappaquiddick Island Association, in his closing statement to commissioners. "Chappaquiddick needs the tools and power [of a DCPC]. It needs your help now, please."

With the designation, a building moratorium will remain in place for one year while new regulations are developed. Edgartown voters will then have to approve those regulations.

According to Steve Ewing of the Edgartown conservation commission, which sponsored the DCPC nomination, the new regulations will focus on protecting water quality, open space and both archaeological and cultural resources.

Commissioners made a special point of adding a guideline that would promote regulations that somehow foster more affordable housing on Chappaquiddick.

While such efforts all sounded like noble gestures, there was no unified applause to welcome the MVC vote last night. Instead, there was a sense of a tight-knit community still torn by bitterly divided testimony at last month's hearing.

Commissioner Jennie Greene lobbied for special provisions that would bring the two sides back to the table as DCPC regulations are drafted. "There's been very bitter opposition, and the community is split," she said. "There might be a method to bring people together and not just a certain few. I want to see this fighting stopped."

But the majority of commissioners would not support any language that appeared to tell Edgartown officials what to do in forming a DCPC committee. "It's insulting to the town," said commissioner Robert Zeltzer.

The two camps in the debate differed over the most basic premise: Was a DCPC even necessary? Opponents argued that there is no hard evidence to back up threats to water quality or infrastructure or even the pressures of development.

"There are assertions that Chappaquiddick is being degraded," said board of health member Bill Elbow. "I'm looking for scientific documentation, and I don't find it."

In her report to the commission, MVC coastal planner Joanne Taylor said the current zoning regulations on Chappaquiddick are more suited to "suburban development." She indicated that both shellfish and water sources needed protection.

Commissioner James Athearn, who chaired the hearing, kept the discussion balanced by alternating between those in favor of the DCPC and those against.

In favor of a DCPC, residents pointed to the proliferation of trophy houses on Chappaquiddick, to the long lines for the Chappy ferry and to concerns for water quality.

Chappy resident Nancy Bettencourt urged commissioners to let Chappaquiddick do what Aquinnah had done over a year ago when it declared a townwide DCPC.

"Our regulations are outdated. We need time to plan," she said. "There's a 6,000-square-foot trophy house on Chappy, clear-cut down to the water. It's dangerous to the rural character, and it drives up the cost of land."

Among the opposition, resentments were still simmering. Richard Ezequelle, who has summered on Chappy for 21 years, said he was a member of Chappaquiddick Island Association but he had never heard of a master plan being developed by the group.

"I found out about it in the Gazette," he said. "There's been a serious lack of communication with the citizens of Chappaquiddick, people not included in the application and development process."

Another resident, Steve Wardell, asked for an apology from fellow Chappy residents who asserted that the water on Manaca Hill was inferior. "My kids were here for the weekend and wouldn't drink the water or brush their teeth with it," he said. "This has created a lot of animosity."

To prove a point, Mr. Wardell brought a supply of coffee to the meeting, made from his home tap water. "Three water experts have said this water quality is acceptable," he said.

In sheer numbers the division was almost equal. The commission received 201 letters and postcards in favor of the district designation. In opposition were 13 letters plus a petition signed by 230 people.

Commissioner Michael Donaroma was one of the few to support an effort to heal the rift by making sure that the next committee to move forward with the DCPC draw viewpoints from both sides. "It will have to be a balanced committee," Mr. Donaroma said, "to pass town meeting floor."