State Assemblyman Martin Garrick will ask the Public Utilities Commission to reconsider its April decision to change North County's area code, a representative from the assemblyman's office said Thursday.

Mike Zimmerman, chief of staff for Garrick, R-Solana Beach, said the assemblyman's office will submit a petition for modification on Friday. The document will formally ask the commission to reconsider its April 24 decision to change North County's area code from 760 to 442.

Zimmerman said he expects the petition to be before commissioners at their Sept. 4 meeting.

In July, Garrick and other local officials signed a joint letter asking the commission to reconsider its decision to split the area code, but Zimmerman said they since have learned that the commission requires either an official appeal or a petition for modification to revisit a past decision.

The deadline to file an appeal passed 30 days after the commission's April 24 decision, weeks before momentum picked up to challenge the decision, leaving the petition as a last option.

The petition for modification requires the petitioner to show proof that new information has come to light since the decision was made. Zimmerman declined Thursday to disclose what that new information was, but he did say many people were upset to learn that the change in area codes would affect mobile phones as well as land lines.

The commission decided to split the 760 area code, which covers about a third of California, because the combinations of numbers that could be used with the code were running out. The new area code is scheduled to begin in November on a voluntary basis and will become mandatory next May, although Garrick also is asking the commission to delay its implementation.

"We have a huge hill to climb here, but Mr. Garrick is absolutely committed to trying to change it," Zimmerman said.

Under the commission's decision, the new 442 area code would be specific to North County and is projected to last 22 years. The change would be the third area code for North County since 1980.

Some North County residents said they felt out of the loop when the commission approved the area code change.

Leucadia resident Scott Chatfield launched the Web site www.Keep760.org in early June to protest the change. So far, more than 5,000 people have used the site to generate letters that ask local elected officials to push the commission to reconsider its decision.

Rather than splitting the 760 area code, Chatfield said he would rather the commission create an overlay zone that would allow everyone to keep their phone numbers, while new phones within the same area would be assigned 442.

Even if he does not win his fight against the commission, Chatfield said he hopes the effort will at least inspire the commission to revise its notification process, as many people said they were unaware that the commission was considering the change.

Zimmerman said Garrick has met with commissioners individually to discuss the issue, and some were more sympathetic than others.

Garrick also has met with an attorney who has experience with the commission to help write the petition for modification, Zimmerman said. With more work ahead, however, the people who have given their energy to keep 760 in North County may be asked to pitch in financially as well

"We are working with some chamber folks and with other people involved," he said. "We're trying to be as frugal as we can, but it's definitely not going to be cheap."

Contact staff writer Gary Warth at (760) 740-5410 or gwarth@nctimes.com.