It will be more difficult for Santa Rosa to avoid annexing small islands of unincorporated county land inside its borders under a policy adopted Wednesday by the agency responsible for setting the local government boundaries.

The city no longer will be allowed to annex only a portion of small islands, defined as those with fewer than 12 registered voters, according to rules adopted Wednesday by the Sonoma County Local Agency Formation Commission.

Instead, new annexation requests will be approved by the commission only if the entire island is brought under city jurisdiction.

The new policy will likely apply to only about a quarter of the 52 such islands in the county, 51 of which are in Santa Rosa. It will not affect the future annexation of the largest island, the 3,500 acres of Roseland that remain outside city's southwest boundary.

"I think it'll provide more clarity and certainty that we can eliminate some of the smaller islands and provide better police and fire service to those areas," said Richard Bottarini, executive director of the commission.

The 11 members of the commission are representatives of the public, the county, and its nine cities and 54 special districts. Their role is to regulate the formation and expansion of government agencies to promote efficient government.

The commission views county islands as an unfortunate consequence of rapid city growth that need to be eliminated to limit confusion and inefficient delivery of services, such as sewer, water and public safety.

The policy shift is a compromise between the status quo, which encourages annexations of entire islands whenever possible but doesn't require it, and a tougher stance some favored to require annexations of entire islands up to 150 acres.

Supervisor Efren Carrillo said he favored the tougher option because he saw it as the commission's role to "push as hard as we could" for a policy that eliminates all the islands.

"The intent is for us to encourage the cities to annex all island of unincorporated territory," Carrillo said.

Chuck Regalia, Santa Rosa's director of community development, pushed back against the "entire island annexations" proposal. He contended that policy would have the opposite of its intended effect because it would impose so many additional costs on property owners that they wouldn't seek annexation.

"When a single applicant is responsible for doing a significant or sophisticated environmental review, it's very expensive," Regalia said.

The city can initiate annexations on its own, but that is a costly, time-consuming proposition that city leaders historically have avoided, he said.

"Numerous councils have not wanted to force annexation on people that weren't committed to it," Regalia said.

Carrillo expressed frustration with that position, suggesting the city should do more than just "sit on it's laurels and wait for folks to request annexation."

The 5th District supervisor, who represents parts of the city's west side, said the city needs to do more than just have a policy supporting annexations -- it needs to have a plan.

"I don't think the city has done an honest job in at least identifying what their long-term trajectory is," Carrillo said.

Supervisor David Rabbitt, who encouraged commission staff to craft a compromise, called it a "middle ground" that would provide an incentive to cities to "nip around the edges" of more annexations while also keeping costs down.

The costs of the smaller annexations are lower because they don't require environmental review, and because they don't trigger elections, Bottarini said.

For islands with fewer than 12 registered voters, only property owners get a say in the annexation, not residents. Such small annexations are harder to block because opponents have to represent more than 50 percent of the assessed value of the land proposed for annexation.

Carrillo expressed disappointment that discussion has stalled between the county and the city about how to transition Roseland from county to city control.

"It feels like its Groundhog Day," he said.

Regalia said the only realistic way such a large annexation is going to happen is if the two agencies work closely together and share planning and environmental costs he estimated at $500,000.

"At this stage of life in California, we don't have that kind of money floating around," Regalia said.

You can reach Staff Writer Kevin McCallum at 521-5207 or kevin.mccallum@pressdemocrat.com. OnTwitter @citybeater.