State Labor and Industry Secretary Harris Wofford, a former adviser to President John F. Kennedy, was chosen Wednesday by Gov. Robert P. Casey to fill Pennsylvania's vacant U.S. Senate seat.

Casey, a Democrat, said at a jammed noontime news conference at the state Capitol that Wofford, also a Democrat, would fill the vacancy caused by the April 4 death of Republican John Heinz and would run for the seat in a Nov. 5 special election.Wofford, 65, previously served as chairman of the state Democratic Party and a civil rights adviser to Kennedy, and was a founder of the Peace Corps and an assodciated director of the corps.

The selection came more than a month after Heinz died in an airplane-helicopter crash near Philadelphia and after a number of other potential candidates withdrew from consideration, including Chrysler Chairman Lee Iacocca.

Lt. Gov. Mark Singel, who lobbied his boss for the job, told his staff today that he did not get it, sources said. Singel, who once said he might challenge Casey's choice for the Democratic Party's nomination, was expected to attend the news conference and announce his support for Wofford.

Casey had said he wanted Singel to remain as lieutenant governor. If Singel had gone to the Senate, the lieutenant governor's duties would have fallen to Senate President Pro Tem Robert Jubelirer, a Republican who is a vocal Casey critic.

Before Heinz's death, Wofford told Casey he was thinking about running in 1992 for the U.S. Senate seat held by Republican Arlen Specter. Singel had already formed an exploratory committee for the 1992 race before Heinz's death changed the political landscape.

Wofford, a lawyer, is said to have the support of a number of Pennsylvania and U.S. labor leaders.