UPDATE 1-Pan Pacific's H1 copper output plan down 2.6 pct from H2

* Firm's planned copper output down as plant closed after quake, tsunami

* Plans to resume operations at closed facility in late April (Adds detail, background

TOKYO, April 6 (Reuters) - Pan Pacific Copper, Japan's biggest copper smelter, said on Wednesday it will produce 2.6 percent less copper in the April-September first-half compared to the preceding six months as one of its three plants will remain shut until late this month in the aftermath of a massive quake.

Two major copper plants, which account for a quarter of Japan's total 1.5 million tonnes output, are currently shut after the March 11 earthquake and tsunami, while No.2 smelter Sumitomo Mining is bracing for a long period of regular maintenance. [ID:nL3E7EV0K0][ID:nL3E7F10EU]

Pan Pacific, part of JX Holdings Inc , said it plans to produce 257,494 tonnes of copper in the April-September first-half of this financial year.

That compares to an estimated 264,485 tonnes in the preceding six months and 293,669 tonnes in the same period a year ago.

The company said it plans to resume operations at its closed Hitachi plant, northeast of Tokyo, in late April.

"We plan to maximise output at our two other plans in west Japan to make up for lost production at Hitachi, given the expected supply squeeze," the company said in a statement.

Pan Pacific said the Hitachi plant will produce 53,430 tonnes in April-September, down 15 percent from the previous six months and down 40 percent from the corresponding period a year earlier.