As Mayor Bloomberg and the City Council toy with the possibility of lengthening term limits, the city’s Campaign Finance Board is working to find a way to resolve the snarl of regulatory issues that a change to the law would create.

The agency is taking seriously the possibility that the council might vote to extend term limits and is crafting a detailed contingency plan, a spokesman for the Campaign Finance Board, Eric Friedman, said.

“We have a lot of people looking at this question,” he said. “We’re aiming to be ready in a month or two with clear guidance for candidates.”

Earlier this month, Council Member Oliver Koppell directed staff to draft legislation that would boost to three from two the number of terms allowable under the limit, and Mr. Bloomberg has said that he would consider signing such a bill.

The ripple effect of legalizing a third term for elected officials would affect dozens of races and create previously unexplored challenges to campaign finance laws. Council members who have been raising money under the city’s public financing program for a citywide office, such as comptroller or public advocate, could suddenly be faced with the prospect of running for re-election and have to comply with lower spending limits than those in place for citywide candidates.

Council candidates, for example, are allowed to spend only up to $161,000 in the primary election and another $161,000 in the general election. Mayoral candidates are allowed to spend as much as $6,158,000 in the primary and $6,158,000 in the general election.

More than a year before the November 2009 election, the speaker of the council, Christine Quinn, a potential mayoral candidate, already has spent $285,535 on her campaign. If term limits were extended and she ran for re-election, her candidacy and those of other candidates who had planned to run for citywide office would pose a new challenge to the Campaign Finance Board.

In addition to current elected officials, the CFB must deal with the glut of candidates for City Council who have been raising money in expectation of running for an open seat created by a term-limited member’s departure. While state candidates have some ability to transfer money between campaigns, city campaign finance laws are stricter, aimed at discouraging the accumulation of campaign “war chests” that are passed from one race to the next. Without new guidelines from the Campaign Finance Board, it would be difficult for city candidates to set aside their campaign funds for a future run.

There are isolated precedents to some of these issues, such as the decision by a former president of the Bronx, Fernando Ferrer, to abort a mayoral run in 1997 in order to run for re-election. In that case, the Campaign Finance Board ruled that a variety of expenses from his mayoral campaign did not apply to his spending limit for the borough president’s race, allowing him to comply with the law.

Despite such case-by-case examples, Mr. Friedman said that a change in term limits would likely require broad new guidelines in order to consistently deal with the much larger number of candidates affected.