Patrick A. (Pat) Deck Jr., 35, died Wednesday at the Veterans Administration Hospital here following a long illness.

He was piloting a troop-carrying helicopter that was shot down in Vietnam in September, 1965. Since then he had been a patient at Walter Reed Hospital and the VA Hospital, under treatment for brain damage and complications.

Born in Washington, Mr. Deck graduated from Bethesda-Chevy Chase High School in 1958. He received a degree in chemical engineering in 1963 from Cornell University, where he rowed with the lightweight crew.

After graduation, he worked as a chemical engineer for the W. R. Grace and Co. plant at Erwin, Tenn., where uranimum waste from the government plant at Oak Ridge was refined.

Mr. Deck was called up by the Army Reserves for active duty in April, 1964. After training as a helicopter pilot at Ft. Rucker, Ala., he was sent to Vietnam in the summer of 1965.

He flew numerous missions in Vietnam before his helicopter was shot down. He received the Purple Heart and the Medal of Valor.

He is survived by his wife, Pamela Manus Deck, of Oxon Hill, whom he married in December, 1964: his parents, Mr. and Mrs. Patrick A. Deck of Chevy Chase, and two sisters. Ellen Nesheim, of Washington, and Margie Deck, of Chevy Chase.