PLAINFIELD, Ind. (AP) _ Hugh A. Barker has announced plans to retire as chairman and chief executive officer of Public Service Indiana early next year.

Barker, who made his announcement to PSI officers and management staff Wednesday morning, had informed the utility's board of directors of his intentions on March 16, said PSI spokesman Michael Goss.

Barker, 62, has served as chief executive of PSI, the state's largest utility, since 1977.

Goss said Vice President Darrell V. Menscer would assume on an interim basis the utility's operating responsibilities, other than the implementation of a new holding company structure.

PSI currently is working under a four-year agreement that alllows the utility to increase rates and write off part of its loss on the Marble Hill nuclear power plant, which was canceled in 1984 after $2.7 billion was spent on its construction.

The utility had been near default before the rate agreement was approved in March 1986 by state regulators, but creditors granted PSI a reprieve after the agreement was negotiated.

PSI serves about 542,000 customers in 69 Indiana counties.