Eugene Keogh, a veteran member of Congress from Brooklyn who was the chief sponsor of the pension-plan legislation that bears his name, died of pneumonia Friday at St. Vincent's Hospital in Manhattan. He was 81.

Keogh, a Brooklyn native, served in Congress for 30 years, representing a heavily Democratic district which included parts of East New York, Canarsie, New Lots, Cypress Hills and Brunswick.Under the Keogh Plan, self-employed people such as doctors, lawyers, salesmen and free-lance writers may, for pension purposes, invest part of their income in a fund that is exempt from federal taxes until the money is withdrawn at retirement. The legislation, which was enacted in 1962, allowed the self-employed to get benefits roughly equal to workers under corporate pension plans.

Keogh received a bachelor's degree from New York University and a law degree from Fordham. He began practicing law in 1932, and three years later served briefly in the New York State Assembly. In 1936, he was elected to the first of his 15 terms in the House of Representatives, where he served on the influential Ways and Means committee.

After his retirement at 59, Keogh worked with the law firm of Halpin, Keogh and St. John, and served as counsel to the firm of Abberley, Kooiman, Marcellino & Clay until early last year.

He is survived by his wife, a son, a daughter and two grandchildren.