A hearing will be held Thursday in City Hall to discuss New Haven’s principal power provider’s decision to leave town.

United Illuminating, which has been delivering electricity to the New Haven since 1899, is relocating everything — operations, equipment, offices, even bucket trucks — to nearby Orange. The move will be made around mid-2012, but already New Haven officials are displeased with the news.

“We’re very upset that UI is leaving town,” Aldermanic President Carl Goldfield said this Monday. “It’s been an important corporate citizen.”

Goldfield said his primary concerns have been whether customers would have to pay for the move and whether their rates would increase as a result. Several aldermen, including Goldfield, have considered looking into setting up a publicly owned utility in New Haven to replace UI.

“It’s worth exploring,” he said, “but it will be a very long and complicated undertaking.”

As it stands, UI has property and equipment in six locations throughout Connecticut, including two in New Haven. Although several aldermen feared the move would cause the company to lay off its New Haven employees, UI spokesman Al Carbone said the company plans to move everything — including employees — from the six dispersed locations to their new headquarters in Orange.

Carbone said Orange was an ideal location because it was “equidistant” to all the cities they serve. And in the end, Carbone added, the move will prove to be “prudent and practical” because the company will only need to pay leases on one location.

He said power rates for 2009–’10 will not be affected by the move. But company officials are unsure whether this will remain true for subsequent years, he said.

“Will people’s rates go up? We don’t know that yet. But there will be savings in the long term,” Carbone said Wednesday.

In response to disapproval from New Haven officials, Carbone said UI will still pay taxes because the company will be leaving equipment here, and that the revenue the city will collect from the company will still be the same. In essence, UI is not “abandoning” New Haven, Carbone said.

UI has written a letter to the Board of Aldermen and invited them to talks with company executives. UI will not, however, be attending the aldermanic hearing later today.

“Our positions have been pretty clear for a long time,” said Carbone.

Environmental groups, business companies and attorneys will be present at the meeting to discuss alternatives to UI as the main provider of electricity to New Haven.